Question

60d+65n=2800 50d+45n=2150

Answer 1

From the second equation we can find that d=43-(9/10)*n
we can put this equation into the first one,
So we have equation 60(43-(9/10)*n)+65n=2800
Solving that we get n=20
60d+65*20=2800
d=25

So the answer is d=25 and n=20