Table:
0
A
B
C
D
E
1
State (class)
Vacator
Reason for change
Successor
Date of successors formal installation
2
Tennessee (1)
Vacant
Vacancy in term
Andrew Johnson ( D )
October 8, 1857
3
South Carolina (3)
Andrew Butler ( D )
Died May 25, 1857
James H. Hammond ( D )
December 7, 1857
4
New Hampshire (3)
James Bell ( R )
Died May 26, 1857
Daniel Clark ( R )
June 27, 1857
5
Texas (1)
Thomas J. Rusk ( D )
Died July 29, 1857
J. Pinckney Henderson ( D )
November 9, 1857
6
South Carolina (2)
Josiah J. Evans ( D )
Died May 6, 1858
Arthur P. Hayne ( D )
May 11, 1858
7
Minnesota (1)
New seat
Minnesota admitted to the Union May 11, 1858
Henry M. Rice ( D )
May 11, 1858
8
Minnesota (2)
New seat
Minnesota admitted to the Union May 11, 1858
James Shields ( D )
May 11, 1858
9
Texas (1)
J. Pinckney Henderson ( D )
Died June 4, 1858
Matthias Ward ( D )
September 27, 1858
10
South Carolina (2)
Arthur P. Hayne ( D )
Successor elected December 2, 1858
James Chesnut, Jr. ( D )
December 3, 1858
11
Oregon (2)
New seat
Oregon admitted to the Union February 14, 1859
Delazon Smith ( D )
February 14, 1859

Questions and formulas:
Question: Where was the successor formally installed on December 3, 1858?
Formula: UNIQUE(CHOOSECOLS(FILTER(A1:E1,E1="December 3, 1858"),1))
Formula2: UNIQUE(CHOOSECOLS(FILTER(A2:E11,E2:E11="December 3, 1858"),1))
Level: medium
Question: Why did the change happen in the state where the formal installation happen on February 14, 1859?
Formula: UNIQUE(CHOOSECOLS(FILTER(A1:E1,E1="February 14, 1859"),3))
Formula2: UNIQUE(CHOOSECOLS(FILTER(A2:E11,E2:E11="February 14, 1859"),3))
Level: medium