The standard form of an ellipse is (x-h)^2/a^2+(y-k)^2/b^2=1
a is the horizontal radius
b is the vertical radius
h is the shift to the right
k is the shift upward
h and k will be shifts left and downward respectively if they are negative. Since the question doesn't mention any shifting we can just let them be 0 so everything is easier. The problem states the vertical axis is 16 and the horizontal axis is 10 so that means a = 10 and b = 16. Now we just plug in.