Question 831570
for the eastbound boat, 
 distance:2(x+7) mile
 speed:(x+7)mi/h
 time: 2h
for the southbound boat,
 distance: 2x mile
 speed: x mi/h
 time: 2 h 

it's a right triangle problem, the hypotenuse is 34 miles apart.
now you can set up the equation using Pythagorean theorem,

(2x)^2+(2x+14)^2=34^2
using quadratic equation to solve for x,
you get x = 8
which is speed (mi/h) of southbound boat.

let me know if you have any questions, adamchen894@gmail.com