Table:
0
A
B
C
D
E
1
Episode
Broadcast date
Run time
Viewers (in millions)
Archive
2
" Episode One "
30January1971
24:39
6.1
Manual colourisation
3
" Episode Two "
6February1971
24:31
8.8
Chroma dot colour recovery
4
" Episode Three "
13February1971
24:30
7.5
Chroma dot colour recovery
5
" Episode Four "
20February1971
24:40
7.4
Chroma dot colour recovery
6
" Episode Five "
27February1971
23:34
7.6
Chroma dot colour recovery
7
" Episode Six "
6March1971
24:48
7.3
Chroma dot colour recovery

Questions and formulas:
Question: When there are  7.4 million viewers how many episodes are there?
Formula: ROWS(UNIQUE(FILTER(A1, D1=7.4)))
Formula2: ROWS(UNIQUE(FILTER(A2:A7, D2:D7=7.4)))
Level: medium
Question: When 24:31 is the run time how many measurements of viewers (in millions) are there?
Formula: SUMIFS(D1,C1,"24:31")
Formula2: SUMIFS(D2:D7,C2:C7,"24:31")
Level: easy
Question: When 24:31 is the run time how many millions of viewers are there?
Formula: SUMIFS(D1,C1,"24:31")
Formula2: SUMIFS(D2:D7,C2:C7,"24:31")
Level: easy
Question: When there are 7.5 million viewers what is the archive?
Formula: LET(query1,SUMMARIZE(E1,SUMX(D1)),FILTER(query1,CHOOSECOLS(query1,2)=7.5))
Formula2: LET(query1,SUMMARIZE(E2:E7,SUMX(D2:D7)),FILTER(query1,CHOOSECOLS(query1,2)=7.5))
Level: hard