Related rates into regards to applications of the derivative.

Stuck on this one.

An airplane leaves a field at noon and flies east at 100 km/h and a second airplane leaves the same field at 1pm and flies south at 150 km/h. How fast are the airplanes separating at 2pm.

So if I do a right triangle.

My Vx right would be 200 and x would be 2 for hours//

My Vy(south) would be 150 and y 1 hour.

My Resultant of Vz is what I am looking for and z is 2.23606.

I am to find Vz and I come up with 245 km/h and the answer is 170 km/h.

Can someone see what I did wrong?? Thanks

Joanne