Math
posted by Kaloy .
Mr. R has some money to buy oranges, if he will buy 15 oranges he will need $90 more, if he will buy 10 oranges he will have $60 left. how much money has mr. R?

Let r=amount of money in dollars Mr. R has
and
x=cost of each orange
We will set up the equations
15x=r+90
10x=r60
You can then solve for r and x by the method of elimination, substitution, or comparison. 
Buying 5 more oranges costs an extra $150. Therefore they cost $30 each.
Buying ten oranges costs $300 and leaves him with $60. Therefore he started out with $360.