Speed and time

Question

A car takes 10 hours to cover a certain distance at a uniform speed.   If the speed has been 18 km more per hour it would have taken 7 hours to cover the same distance. Find the distance. 

Answer 1

d=r*t

d=r*10

d=(r+18)*(7)

10r=7(r+18)

10r=7r+126

10r-7r=126

3r=126

r=126/3

r=42 km per hr

d=42*10=420 km, or...

d=(42+18)*7

d=60*7=420 km again