Question 40666
600/X=(600/X+20)-1 OR 600/X=(600-X-20)/(X+20) OR 600X-X~2-20X=600X-12,000 OR 
-X~2-20X=-12,000 OR X~2+20X-12,000 OR (X-100)(X+120)=0 OR X=100 MPH

THEN X+20=120 MPH 

PROOX 600/100=6 HOURS & 600/120=5 HOURS 6-5=1 HOUR LESS @ 120 MPH.