Question 601329
let x be the original speed of the crew
let c be the speed of the current 
speed = distance/time
with hte current : speed = x +c 
x+c = 11/2
with speed against current :
speed = x-c
x-c = 5/2
sove the two equations:
x = 4 
c = 3/2 = 1.5 mph