Table:
0
A
B
C
D
E
1
Interregnum began
Interregnum ended
Duration
Count Palatine of Saxony
Count Palatine of the Rhine
2
9 December 1437 death of Sigismund
18 March 1438 election of Albert II
3 months, 9 days
Frederick II, Elector of Saxony
Louis IV, Elector Palatine
3
27 October 1439 death of Albert II
2 February 1440 election of Frederick III
3 months, 6 days
Frederick II, Elector of Saxony
Louis IV, Elector Palatine
4
12 January 1519 death of Maximilian I
17 June 1519 election of Charles V
5 months, 5 days
Frederick III, Elector of Saxony
Louis V, Elector Palatine
5
20 January 1612 death of Rudolph II
13 June 1612 election of Matthias
4 months, 24 days
John George I, Elector of Saxony
Frederick V, Elector Palatine
6
20 March 1619 death of Matthias
28 August 1619 election of Ferdinand II
5 months, 8 days
John George I, Elector of Saxony
Frederick V, Elector Palatine
7
2 April 1657 death of Ferdinand III
18 July 1658 election of Leopold I
15 months, 16 days
John George II, Elector of Saxony
Ferdinand Maria, Elector of Bavaria
8
17 April 1711 death of Joseph I
12 October 1711 election of Charles VI
5 months, 25 days
Frederick Augustus I, Elector of Saxony
John William, Elector Palatine
9
20 October 1740 death of Charles VI
14 January 1742 election of Charles VII
14 months, 25 days
Frederick Augustus II, Elector of Saxony
Charles Albert, Elector of Bavaria
10
20 January 1745 death of Charles VII
13 September 1745 election of Francis I
7 months, 24 days
Frederick Augustus II, Elector of Saxony
Maximilian III, Elector of Bavaria
11
20 February 1790 death of Joseph II
30 September 1790 election of Leopold II
7 months, 10 days
Frederick Augustus III, Elector of Saxony
Charles Theodore, Elector of Bavaria

Questions and formulas:
Question: What is the number of interregnum for duration 3 months, 6 days?
Formula: ROWS(UNIQUE(FILTER(B1, C1="3 months, 6 days")))
Formula2: ROWS(UNIQUE(FILTER(B2:B11, C2:C11="3 months, 6 days")))
Level: medium