7. Jorge leaves 2 hours early, and is going 20 miles per hour. So before Marcos starts going, Jorge has gone 40 miles (2*20). Then, 1 hour later, Jorge is at 60 miles and Marcos is at 40 (because he goes 40 miles per hour in his car). Another hour later, Jorge is at 80 (60+20) and Marcos is at 80 as well (40 + 40). They will both have gone 80 miles when Marcus catches up.
8. You want to get <em>a</em> isolated.
A = h/2(a + b)
First, multiply both sides of the equation by the reciprocal of h/2.
