I need help in working this word problem out. I need help coming up with the answer because I have no idea what so ever of how to solve this.

Question

850 douglas fir and ponderosa pines in a section of a forest brought by Watts Tree Company. Watts Trre Company paid $300 for each douglas fir and $225 for each ponderosa pines. If Watts Tree Copmany paid $217,500 for the trees, how many of each did Watts Tree Company purchased?

Let x be the number of Doug firs cut. the 850 - x pines were cut.
300 x + 225 (850-x) = 217,500
Solve that equation for x.
75 x = 217,500 - 180,000 = 36500
x = ?