Two fishing boats depart a harbor at the same time, one traveling east, the other south. the eastbound boat travels at a speed 1 mi/h faster than the southbound boat. after 5 h the boats are 25 mi apart. find the speed of the southbound boat.

they are travelling at right angles to each other.
 At any given instant they form a right triangle with their starting point
 South bound = x  [mi/h]
 East bound  = x+1 [mi/h]
 after five hours they will be
 d=5x
 and
 d=5(x+1)
 miles away from the starting point 
 (5x)^2+(5(x+1))^2=625
 25x^2+(5x+5)^2=625
 25x^2+25x^2+50x+25=625
 50x^2+50x-600=0
 x^2+ x - 12=0
 (x+4)(x-3)=0
 take the postive value
 x= 3 mph the speed of south bound
 4mph east bound 

Ithink the answer is d i hope it my friend message me if i’m wrong and i’ll change my answer and fix it for you