Answer:
$1230 
Step-by-step 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