find the difference in the areas of the large and small rectangles

Question

the larger square, the length of it is 7x-12 and the width is 3x

for the smaller square the width of it is 4 and the length is 4x(raised to the 2nd) -3x+7

Answer 1

7x-12=3x

x=3

3x=9

area of larger square=9^2=81

the"smaller square's area = 4^2 = 16

difference in the squares' areas = 81-16= 65

for the smaller square

4x^2-3x+7=4

4x^2-3x+3=0

x=3/8 +/-(1/8)sqr(9-112) which = an imaginary number

but irrelevant to the problem