Let y represent Tim's age and let x represent Chris's age.
y=3x
y=x+14
Set the two equations equal to each other:
3x=x+14
Subtract the x from the one side to get it on the other side.
2x=14
Divide by 2 on both sides
14/2=7
x=7
Plug it back in and see if it works:
y=3(7)=21
Other equation:
7+14=21
x=7
y=21