Question

Farmer Brown planted corn and wheat on

370 acres of his land. The cost of planting
and harvesting corn, c, is $280 per acre. The
cost of planting and harvesting wheat, w, is
$135 per acre. If Farmer Brown's total cost
was $83,300, how many more acres of corn
than wheat did he plant?
no c+w=370
c
280c + 135w = 83,300

Answer 1

So you have the system of equations:
C+W=370. Multiply by -135 to remove w
280c+135w=83,300

-135c-135w=-49950
280c+135w=83,300

Add together:
-135c+280c=33,350. W is gone
145c=33,350
c=230.

And substitute c in any of equations to get w:

C+W=370.
230+w=370
W=140.