Please help with this problem Norman stated across a lake 10

Please help with this problem: Norman stated across a lake 10 miles wide in is fishing boat at 12 miles per hour. After his motor went out, he had to row the rest of the way at only 3 mph. If he was rowing for half the time that the total trip took, how long did the total trip take?

Solution

Let t = total time to get across the lake
then
t/2 = time he was rowing
t/2 = time he was using the motor
.
12(t/2) + 3(t/2) = 10
Multiply both sides by 2:
12t + 3t = 20
15t = 20
t = 20/15
t = 4/3
t = 1 and 1/3 hours (total time)
or
1 hour 20 minutes