3u = 14 - 4u what number is the variable?

According to statistics a person will devote 32 years to sleeping and watching tv. the number of years sleeping will exceed the number of years watching tv by 18. over a lifetime, how many years will the person spend on each of these activities

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?

Answer asap evaluate 4-0.25g+0.5h4−0.25g+0.5h when g=10g=10 and h=5h=5.