The cost of 12 oranges and 7 apples is $5.36. eight oranges and 5 apples cost $3.68. find the cost of each

Oranges=r
apples=a

12r+7a=5.36
-12r       -12r
What you do on one side you do on both sides
12 on the left cancels out
7a=5.36-12r
/7   /7     /7
Divide 7
7 on the left cancels out
5.36/7=0.76
left with
a=0.76-12r/7
so the apples cost $0.76 each
to get the cost of the oranges (r) you do the same as you did to get the cost of the apples.
 
Also on the other equation for 8 oranges and 5 apples you might get different answers but you will see that they are close/similar to the same answers as you will get for the last equations.

Ineed on quadratic equations to solve problems