A boat must head due north across a river channel that has a current of 9 km/hr towards the west. The boat is capable of traveling at 28 km/hr in still water. If the boat heads into the current to keep its true north course, what will be the resultant velocity of the boat?

Question

A boat must head due north across a river channel that has a current of 9 km/hr towards the west. The boat is capable of traveling at 28 km/hr in still water. If the boat heads into the current to keep its true north course, what will be the resultant velocity of the boat? 
I'm really having trouble with this problem. After finding the resultant, you have to find how long it will take to cross.

Henry · Answer

Vc + Vb = Vbc. =9 + Vb = 28i. Vb = 9 + 28i = 29.4km/h[72.2o] N. of E. = 17.8o E. of N.