Given that 6x + y = 15, the value of 3x can be written in terms of y as ay + b for some numbers a and b. What is the simplified value of a + b?
6x = -y+15
3x = -1/2 y + 15/2
a = -1/2
b=15/2
-1/2+15/2=14/2
14/2 = 7
