Find original speed and his speed during the rainfall

Question

Bob drove to portland, a distance of 300 miles. During the last 80 miles his trip, heavy rainfall forced him to decrease his speed by 15 miles per hour, If his total driving time was 6 hours , find his orginal speed during the rainfall

Answer 1

t = d / r

t_{first part} = 220 / r

t_{second part} = 80 / (r - 15)

t_{first part} + t_{second part} = 6

Can you solve for t and answer?