Ineed on how much. will he spend on the cell phone 3 in years

$1230 

Explanation:
First of all, your initial equation is wrong. It should be:
cost = 30m + 150 

To find how much 3 years will cost you have to first find how many months are in 3 years:
12 • 3 = 36 
Then substitute 36 for m in the equation: 
cost = 30(36) + 150
Then solve: 
C = 30(36) + 150 
C = 1080 + 150 
C = 1230 

Y=30x+150 you put 3 in for x which is y=30(3)+150                                                       y=90+150                                                                                                               y=240

He was paid 23 dollars for each lawn