Question 56696
Note that in both cases, you and your friend both travelled for equal amounts of time
Let your friend's speed = X
Your speed = X+20
Time taken to cover 210 = {{{210/(X+20)}}}
Time taken to cover 150 = {{{150/X}}}
Since time is equal
{{{210/(X+20)}}} = {{{150/X}}}

Simplifying you get X = 50

Therefore time = {{{150/50}}} = 3hours