Let x = Ralph's speed. Jim's speed is x + 4. In 45 minutes, Jim travels 45 * (x + 4) = 45x + 180 miles. In 45 minutes, Ralph travels 45 * x = 45x miles. Jim and Ralph are 24 miles apart, so 45x + 180 = 45x + 24. 180 = 24. x = 6 mph. Ralph's speed is 6 mph. Jim's speed is 6 + 4 = 10 mph.