The following table shows the length and width of two rectangles:
length width
rectangle a x + 8 x − 1
rectangle b 4x + 5 3x − 2
which expression is the result of the perimeter of rectangle b minus the perimeter of rectangle a?
a. 10x − 12
b. 18x + 32
c. 10x − 8
d. 18x + 6

The perimeter of these can be found by adding length and width and then multiplying by two. 

Rectangle A: (with all of the variables already doubled)
2x + 16 + 2x - 2 
2x + 2x + 16 - 2
4x + 14
So rectangle A's perimeter is 4x + 14.

Rectangle B: (Still with all the variables already doubled)
8x + 10 + 6x - 4
8x + 6x + 10 - 4
14x + 6
So rectangle B's perimeter is 14x + 6

And now to subtract the two.
(7x + 3) - (4x + 14)
14x + 6 - 4x - 14
14x - 4x + 6 - 14
10x - 8

So it would be C.