From my understanding you ahould use the trig function cos to solve this. cos(c) = 15/25 or 0.6 if you have this following function on your calculator I suggest using it:
cos ^{ - 1}
by using the function like so:
cos^{ - 1} (0.6
you should get about 53.13° (rounding to the nearest hundredth) Hope this helped.
.33 with a line over the .33 because it is not able to be simplified into a whole decimal when ever both numbers are a factor of 3 besides when it is half that will happen