im having trouble doing a trig coeffecient.

t'' + 2t' +6x = 10 cos 3t

i got the homogenius side, but now im having trouble with the right. Any help would be appreciated.

*edit*

I did get it to -3 A cos (3t) - 3Bsin (3t) - 6A sin (3t) + 6b cos (3t) = 10 cos 3t