So far I have figured out the following:
maximize 0.02x1 + 0.01x2 +0.06x3 + 0.07x4
subject to:
xi <= 200,000
xi >= 24,000
x3 <= x2 +x4
x1 >= x3
But when I try to solve this in solver, I get an error which means my contraints must be wrong. Any suggestions on what constaints to put?