First, let's write two expressions, letting x= the number of months which have elapsed:
Bill: 120 + 10x
Phil: 150 + 4x
If we set them equal to each other, then solve for x, that will be the number of months where their weights equal each other:
120+10x = 150 + 4x [starting equation]
-120 -4x -120 -4x [ subtract 120 from both sides, and 4x from both sides, to isolate the term with the variable]
<u>6x</u> = <u>30</u> [divide both sides by 5]
5 5
x=6. They will weigh the same in six months.
