This question can be solved using a system of equation, which requires translating the above word problem into something that can be algebraically
Let O=oranges and Let G=Grapefruit
3O + 2G=85
To solve, you must isolate one of the variables and then work from there. To do that multiply both sides of the bottom or second equation by four and then subtract the bottom equation from the top.
Which would look like this
12O + 8G= 340
Then subtract the bottom from the top to get this
Solving for O we divide both sides by -7, and end up with O=15
Plugging that value back into one of our original equations to solve for G we get this
3(15) + 2G= 85
So 1 case of each altogether would equal 15+20, or $35.