Final answer:
By setting up an equation accounting for the weight gain of Bill and Phil each month and solving for M, we find that it will take 5 months for Bill to weigh as much as Phil.
Step-by-step explanation:
To find out when Bill will weigh the same as Phil, we can set up an equation that represents their respective weights over time. Let M represent the number of months it will take for Bill and Phil to weigh the same. Bill's weight increases by 10 lb each month, and Phil's weight increases by 4 lb each month. We can create two expressions to represent their weights after M months:
Bill's weight after M months: 120 lb + 10M
Phil's weight after M months: 150 lb + 4M
To find when their weights will be equal, we set the two expressions equal to each other and solve for M:
120 + 10M = 150 + 4M
Subtracting 4M from both sides:
120 + 6M = 150
Subtracting 120 from both sides:
6M = 30
Dividing both sides by 6:
M = 5
Therefore, it will take 5 months for Bill to weigh the same as Phil, which corresponds to choice A.