The perimeter P of a rectangle with length l and width w is:

2l + 2w = P

We're given P = 372 and l = 99, so we have:

2(99) + 2w = 372

2w + 198 = 372

**Step 1: Group constants:**

We need to group our constants 198 and 372. To do that, we subtract 198 from both sides

2w + 198 - 198 = 372 - 198

**Step 2: Cancel 198 on the left side:**

2w = 174

**Step 3: Divide each side of the equation by 2**

2w/2 = 174/2

w =

**87**