Answer:
5 months
Step-by-step explanation:
Equate the formulas for the weights of the two boys:
J's weight = 120 lb + (10 lb/mo)m = D's weight = 150 lb + (4 lb/mo)m
Solve as follows: Subtract 120 lb from both sides:
(10 lb/mo)m = 30 lb + (4 lb/mo)m.
Then: (6 lb/mo)m = 30 lb, and m = (30 lb) / (6 lb/mo) = 5 months
