If Teresa drove 936 miles in 13 hours, this would mean she would have driven 72 miles every hour. 72 times 9 equals 648. After 9 hours, she would have driven 648 miles.
Number of blue shirts on sale = (3/5)(2x/3) = 2x/5 .
Number of medium sized blue shirts on sale = (1/5)(2x/5) = 2x/25 .
Fraction of the shop's T-shirts are blue T-shirts that are on sale and are size medium = = 2/25 . ( Number of medium sized blue shirts on sale divided by total number of T-shirts )
There are 714 boys in that school, you can cross multiply and divide to find the answer, if you wanna check. The way I wrote it was x (boys) / 1309 = 6/11.