When they give you an x,y magnitudes, you are loking for the resultant HYPOTENUSE of a right triangle....first sketch the x and the y components, then use the pythagorean theorm to find the hypotenuse...
First one x magnitude =6 y magnitude = -10 hypotenuse = sqrt(6^2 + 10^2) = 11.66
the angle will be in the FOURTH quadrant (because y is negative)
and is equal to arctan (-10/6) = -59 degrees
Do you see how it is done? Try the second one!