Joe can paint a wall by himself in 150 minutes. suppose steve can paint a wall 4 times the rate as joe. how long will it take both steve and joe to paint the same wall?

Joe can paint 1 wall in 150 minutes. 
Since Steve can paint a wall 4 times the rate as Joe, Steve can paint a wall 150 minutes divided by 4.
150/4 is 37.5.
Steve can paint a wall in 37.5 minutes, a difference of 112.5 minutes.
Hope this helps :)