$312 to power-wash + $12 /w
power clean $36/w
Ok
312 + 12w > 36w
312 > 36w - 12w
312 > 24w
312/24 > W
13 > w
13 windows, let's check
312 + 12w > 36w
312 + 12(13) > 36(13)
312 + 156 > 468
468 > 468 with 13 windows the cost is the same
then, use 14 windows
312 + 12(14) > 36(14)
312 + 168 > 504
480
The answer is 12 windows
312 + 12(12) > 36(12)
312 + 144 > 432
456 > 432 12 windows