Question 856332
Do you mean the width is 12x+3 or 2x+3??
12x^2 + 10x - 12 
 *[invoke change_this_name4450 12, 10, -12, "x"]
2*(6x^2+5x-6)
6x^2+2x+3x-6

2 (3x-2) (2x+3)
(6x-4)*(2x+3)
the length is (6x-4)