The question is already solved, but I am adding a response so it won't show up on the unanswered list.
Raw material for 500 units per week = 500 x $10 = $5000
Cost of hiring 20 workers per week = 20 x 40 x 25 = $12000
Rental = $2250
Total = 5000 + 12000 + 2250 = $19 250
8.5x-26.35=-37.35
8.5x=-37.35+26.35
8.5x=-11
X=-11/8.5
X=-1.29