Factored out a c and got:
add sin to both sides
now square both sides
get on one side
use quadratic formula to find cos(Ct)
one of the answers is -3.3ish which isn't possible
for cos and the other is .30277 which is possible for cos
so use that one.
arccos(.30277) = 1.26 radians
just plug that answer back in to make sure i didn't screw up. Im pretty high right now so who knows? When ever you're doing trig stuff and theres sines and cosines all over the place, it helps to get all sines or all cosines with the help of identities. Practice makes perfect so don't stop hammering those problems.