Harvey runs a 30-mile course at a constant rate of 4 miles per hour. If Clyde runs the same track at a constant rate and completes the course in 90 fewer minutes, how fast did Clyde run?

GMAT QUANT Problem Solving level 600, Distance/Rate Problems
Harvey runs a 30-mile course at a constant rate of 4 miles per hour. If Clyde runs the same track at a constant rate and completes the course in 90 fewer minutes, how fast did Clyde run?

A. 4.5 miles per hour
B. 5 miles per hour
C. 5.5 miles per hour
D. 6 miles per hour
E. 7 miles per hour