A manufacturer produces a certain men's athletic shoe in integer sizes from 8 to 17. For this particular shoe, each unit increase in size corresponds to a 1/5-inch increase in the length of the shoe. If the largest size of this shoe is 30% longer than the smallest size, how long, in inches, is the shoe in size 15?
Choose the correct choice from the following
A) 6.8 B) 7.4 C) 7.7 D) 8.2 E) 8.6

Rationale: "let x be the length of the size 8 shoe . then 0.3 x = 9 / 5 x = 90 / 15 = 6 inches the size 15 shoe has a length of 6 + 7 / 5 = 7.4 inches the answer is b ."
Answer: B