Answer
See below.
Work Step by Step
One of them will be $30t$, the other one will be $40t$ from the junction and these routes are perpendicular to each other, thus by Pythagorean's theorem: $d(t)=\sqrt{(30t)^2+(40t)^2}=\sqrt{900t^2+1600t^2}=\sqrt{2500t^2}=50t$
