Answer:
Recall the following result:
In a rectangle ABCD, the diagonals AC and BD are equal to each other, that is, AC = BD.
Consider the following statement:
and BD =4-c
The objective is to find the length of each diagonal.
As per the result:
In a rectangle ABCD:
AC = BD
Substitute the given values:

Multiply both sides by 3:

Simplify:
c = 12-3c
Add 3c to both sides :
4c= 12
Divide both sides by 4;
c = 3
Then,
BD=4-3 = 1
Therefore, the length of each diagonal is, 1.