Table:
0
A
B
C
D
1
policy id
policy type code
customer phone
available policies
2
246
Life Insurance
+16(2)5838999222
3
257
Property Insurance
242.763.9214
4
300
Property Insurance
1-416-503-7735x94204
5
301
Property Insurance
(777)537-7792
6
346
Mortgage Insurance
1-446-940-9907x257
7
366
Mortgage Insurance
(379)862-8274x12620
8
472
Mortgage Insurance
+85(6)1302858396
9
583
Travel Insurance
1-797-927-3585x9321
10
586
Life Insurance
991.642.6485x822
11
630
Property Insurance
813.178.8211x557
12
636
Life Insurance
889-572-0609x552
13
751
Life Insurance
1-138-841-3073
14
879
Mortgage Insurance
1-381-132-0127x3801
15
927
Mortgage Insurance
00481937923
16
993
Property Insurance
405.090.8654x021

Questions and formulas:
Question: Show all customer phone numbers
Formula: UNIQUE(C1)
Formula2: UNIQUE(C2:C16)
Level: easy
Question: Customer phone numbers
Formula: UNIQUE(C1)
Formula2: UNIQUE(C2:C16)
Level: easy
Question: the life insurance policy ids and their corresponding customer phones
Formula: LET(query1,FILTER(A1:D1,B1="life insurance"),UNIQUE(CHOOSECOLS(query1,3,1)))
Formula2: LET(query1,FILTER(A2:D16,B2:B16="life insurance"),UNIQUE(CHOOSECOLS(query1,3,1)))
Level: hard
Question: the phone and policy id of customer who has bought life insurance
Formula: LET(a,HSTACK(C1,A1),b,C1,c,CHOOSECOLS(UNIQUE(CHOOSECOLS(FILTER(A1:D1,B1="life insurance"),3)),1),UNIQUE(FILTER(a,NOT(ISNA(XLOOKUP(b,c,c))))))
Formula2: LET(a,HSTACK(C2:C16,A2:A16),b,C2:C16,c,CHOOSECOLS(UNIQUE(CHOOSECOLS(FILTER(A2:D16,B2:B16="life insurance"),3)),1),UNIQUE(FILTER(a,NOT(ISNA(XLOOKUP(b,c,c))))))
Level: hard
Question: Which type has the most available policies? 
Formula: TAKE(SORT(SUMMARIZE(B1,DCOUNTX(D1)), 2, -1), 1)
Formula2: TAKE(SORT(SUMMARIZE(B2:B16,DCOUNTX(D2:D16)), 2, -1), 1)
Level: hard
Question: Which policy type has more than 4 customers?
Formula: LET(query1,SUMMARIZE(B1,SUMX(C1)),FILTER(query1,CHOOSECOLS(query1,3)>4))
Formula2: LET(query1,SUMMARIZE(B2:B16,SUMX(C2:C16)),FILTER(query1,CHOOSECOLS(query1,3)>4))
Level: hard
Question: Policies types with at least 4 customers 
Formula: LET(query1,SUMMARIZE(B1,SUMX(C1)),FILTER(query1,CHOOSECOLS(query1,3)>=4))
Formula2: LET(query1,SUMMARIZE(B2:B16,SUMX(C2:C16)),FILTER(query1,CHOOSECOLS(query1,3)>=4))
Level: hard
Question: Any customer phones?
Formula: UNIQUE(C1)
Formula2: UNIQUE(C2:C16)
Level: easy
Question: the customer phone
Formula: UNIQUE(C1)
Formula2: UNIQUE(C2:C16)
Level: easy
Question: the phone and policy id of customer under life insurance
Formula: LET(query1,FILTER(A1:D1,B1="life insurance"),UNIQUE(CHOOSECOLS(query1,3,1)))
Formula2: LET(query1,FILTER(A2:D16,B2:B16="life insurance"),UNIQUE(CHOOSECOLS(query1,3,1)))
Level: hard
Question: The type having the most available policies.
Formula: TAKE(SORT(SUMMARIZE(B1,DCOUNTX(D1)), 2, -1), 1)
Formula2: TAKE(SORT(SUMMARIZE(B2:B16,DCOUNTX(D2:D16)), 2, -1), 1)
Level: hard
Question: The policy types shared by more than 4 customers.
Formula: LET(query1,SUMMARIZE(B1,SUMX(C1)),FILTER(query1,CHOOSECOLS(query1,3)>4))
Formula2: LET(query1,SUMMARIZE(B2:B16,SUMX(C2:C16)),FILTER(query1,CHOOSECOLS(query1,3)>4))
Level: hard