trig: convert rectangular coordinates to polar

I have the following question from a practice test, but my answer does not match any of the choices.

Convert x=7,y=-24 to polar coordinates. Please show your logic.

Choices:

a) (r,theta) = (625,73.74)
b) (r,theta) = (25,73.74)
c) (r,theta) = (625,4.99)
d) (r,theta) = (25,4.99)


I get r = sqrt(7^2+(-24)^2)=25

For theta, I get -73.74 degrees (not one of the answers)