walking at 3/4 of his usual speed,

Question

a man is late by 2.5 hrs. What is he usual time?

Answer 1

3/4 speed takes 4/3 the usual time.

So,
4/3 x = x + 2.5
1/3 x = 2.5
x = 7.5

Answer 2

usual speed --- x km/h
time at usual speed to go 1 km = 1/x hrs

time at 3/4 his normal speed = 1/(3x/4) = 4/(3x)

4/(3x) - 1/x = 2.5
times 3x
4 - 3 = 7.5x
7.5x = 1
x = 1/7.5 = 2/15 km/h

Answer 3

Steve's answer and mine seem to contradict each other, but we defined x differently.
Steve defined x as his usual time, so the answer of 7.5 is correct for his usual time

I defined x to be the usual speed, and got x = 2/15
so to go 1 km would take
1/(2/15) = 15/2 = 7.5 , the same as Steve.