Final answer:
To find out how many months it will take for Joseph to weigh the same as Keith, we set up an equation and solve for m. The correct answer is a) 6 months.
Step-by-step explanation:
To find out how many months it will take for Joseph to weigh the same as Keith, we need to set up an equation. Let m represent the number of months. The total weight of Joseph after m months will be 120 + 10m, and the total weight of Keith after m months will be 150 + 4m. We can set up the equation as follows: 120 + 10m = 150 + 4m. Solving for m, we get: 6m = 30. Dividing both sides by 6, we find that m = 5. So it will take 5 months for Joseph to weigh the same as Keith. The correct answer is a) 6 months.