Walking at $\frac{3}{4}$ of her usual speed, Priyanka reaches the metro station 15 minutes later than usual. What is her usual time to walk to the station?

Explanation

1. 01

   At $\frac{3}{4}$ of the speed, time becomes $\frac{4}{3}$ of the usual time $T$.

2. 02

   Extra time $= \frac{4}{3}T - T = \frac{T}{3} = 15$ min.

3. 03

   $T = 45$ min.