Answer:
2.5x + 120 = -3.5x +220; after about 16.6 weeks Roy and Luis will weigh the same amount in pounds
Explanation:
Roy's: y = 2.5x + 120
Luis': y = -3.5x + 220
x is representing the number of weeks and y is representing the total number of pounds each will weight after x weeks.
1) set the two equations equal to each other because you want them to weigh the same amount (this might be your equation if they don't want you to solve for the number of weeks)
2.5x + 120 = -3.5x +220
2) Solve for x to find after how many weeks they will weigh the same
2.5x = -3.5x +100
6x = 100
x = 16.6667 weeks