Four apps and two e-books cost $18. Five e-books and three apps cost $31. What is the cost of one app?
+36916 4a + 2e = 18
3a + 5e = 31 multiply first equation by -2.5 to get
-10a -5e = -45 add bottom two equations ( this will eliminate the 'e' variable)
- 7a = -14
a = 2 dollars
