Math Question

Let 2x(km/h)be his running speed
and x(km/h) be his walking speed.

2x*2+3*x=21
4x+3x=21
7x=21
x=3

∴His walking speed is 3km/h.

Peter's running speed is twice his walking speed.
running for 2 hours such as walking for 4 hours.
walking for (4+3)hours and tavelled 21km
that means he walks 3km per hour

Let xkm/h Peter's walking speed , then his running speed is 2xkm/h
(2x)2 + 3x=21
4x + 3x=21
7x=21
7x/7=21/7
x=3
so.Peter's walking speed=3km/h