Question 63898
Suppose : 
x is the original side of the square
L is area of the original square
Ln is area of the new square
so,
L = x^2
Ln = (x+3)^2
L + 39 = x^2+6x+9
x^2 + 39 = x^2+6x+9
39 = 6x + 9
39 - 9 = 6x
30 = 6x
5 = x

Conclude: the dimension of the original square is 5 inches x 5 inches