Answer
T=$\frac{40}{x}$+$\frac{40}{x+30}$
T(30)=2 hours
Work Step by Step
The total time, T, can be expressed as equalling the outgoing time ($\frac{40}{x}$) plus the return time ($\frac{40}{x+30}$).
T(30)=$\frac{40}{30}$+$\frac{40}{30+30}$
T(30)=$\frac{4}{3}$+$\frac{2}{3}$
T(30)=2 hours