I am confused! Help!

Question

It took Fran 3.6 hours to drive to her​ mother's house on Friday morning. On her return trip on Saturday ​night, traffic was​ heavier, so the trip took her 4 hours. Her average speed on Saturday was 3mph slower than on Friday. What was her average speed on Saturday​?

Answer 1

Let r = her Fri speed, then r-3 = her Sat speed.

Distance = rate * time and she went the same distance on both days.

3.6r = 4(r-3)

.4r=12 and r = 30 and her Sat speed is 27