Ok... we'll do the same here, elimination
g = carbs in one glass of milk
b = carbs in a snack bar

in this, we can simply multiply by -2 at the bottom to get a -4g, and thus "eliminate" the g-variable
3+7=10
55/10=5.5
5.5 x 3=16.5
5.5 x 7=38.5
16.5 : 38.5
The answer is b .........
The formula for perimeter is 2L + 2W and the formula for the area is L * W, since we don't know the width we will divide 35:7 = 5 and he the measurement for the width.
Now just add L + W = 12 and multiply by 2 the answer is 24
Or 2 * 7 + 2 * 5 = 24