A boat traveled upstream 90 miles at an average speed of (v-3) miles per hour and then traveled the same distance downstream at an average speed of (v+3) miles per hour. If the trip upstream took a half hour longer than the trip downstream, then how many hours did it take the boat to travel downstream?  Answers.
A) 2.5	B) 2.4	C) 2.3	D) 2.2	E) 2.1

Rationale: 90 / ( v - 3 ) = 90 / ( v + 3 ) + 0.5 hours = > 90 ( v + 3 ) = ( v - 3 ) [ 90 + 0.5 v + 1.5 ] 90 v + 270 = ( v - 3 ) ( 183 / 2 + v / 2 ) 180 v + 540 = ( v - 3 ) ( 183 + v ) = 183 v - 549 + v ^ 2 - 3 v v ^ 2 - 1089 = 0 = > v = 33 miles / hr = > time downstream = 90 / 36 = 30 / 12 = 5 / 2 = 2.5 hrs answer a 2.5
Answer: A