Question 770019
One of the keys is , "While the faster,... the second...".  The amount of time is the same time interval.  Call the time quantity, x hours.


CAR_________RATE_________TIME__________DISTANCE
Slow________r____________x_____________60
Fast_______r+40__________x_____________70


Make expressions for x for each car using r*t=d:

CAR_________RATE_________TIME__________DISTANCE
Slow________r____________60/r_____________60
Fast_______r+40__________70/(r+40)_____________70


The time quantities being equal, we just show the equation:
{{{60/r=70/(r+40)}}}  and solve for r.
... and of course, r+40.