Answer:
15 inches
Step-by-step explanation:
As the square cake was cut in two equal pieces, we have that one side of the rectangle is the double of the other side, so we have that:
2*Length + 2*Width = 45
Length = 2*Width
So using the value of length in the first equation, we have:
4*Width + 2*Width = 45
6*Width = 45
Width = 7.5
Length = 2*Width = 15
So each side of the original cake is equal to the length of the rectangle pieces, that is, 15 inches.