This is correct because when setting up this sentence as an equation, you need to look at the numbers and how they're used. There are independents and dependents.
indep.:
12,16
dep.:
1.50,0.50
Furthermore, there are 1 of each on both sides of the equation, match them from the equation by name and you get the answer.
Assuming the length is y and the width is x Perimeter = y + y + x + x = 2y +2x = 2 (y + x) if the is 8 and the perimeter is 108 108 = 2 (y +8) 108/2 = y+8 54 = y +8 54 - 8 = y 46 = y