If it takes Matthew an hour to get to his friends house, and two hours if he drives 25 mph slower, how far away does Matthews friend live?

speed = distance/time

distance = speed * time

d = st

Let distance = d; faster speed = s; t = time

At the faster speed:

d = s * t

d = s * 1

d = s

At the slower speed:

d = st

d = (s - 25)* 2

d = 2s - 50

We now have two equations,

d = s
d = 2s - 50

We can equate the right sides

s = 2s - 50

-s = -50

s = 50

The faster speed is 50 mph.
It takes him 1 hour at the faster speed.

d = st

d = 50 mph * 1 hr

d = 50 miles

Answer: the distance is 50 miles