Answer:
You can find this by multiplying 150 by 18 to see how much monney he needed for his original goal:
150 times 18 = $2700
After 10 months he saves $1200 , which means to find out how much money he needs to save up for $2700, you will subtract 1200 from 2700:
2700 - 1200 = 1500
He still needs $1500. Which should take, 10 months since he saves $150 a month and 1500/150 = 10.
Explanation:
Hope it helps! =D