Let x be the distance averaged at 68 mph and let y be the distance averaged at 52 mph. Then your mathematical model consists of these two equations x + y = 330 miles (1) (the total distance equation)+ = 5.3 hours. (2) (the total time equation). Solve it to get the answer. You also can to reduce the Math model to the only one single equation + = 5.3. Either model will bring you to the same final result.