Quick question what is the antiderivative of 3sinxcosx?

I guess when you say antiderivative you mean integral because integral is opposite of derivative.
∫3sinxcosxdx = 3∫sinxcosxdx       now we take that replacement: sinx = t
                                                                                         now we derivative
                                                                                                      cosxdx = dt

3∫tdt = 3(t^2)/2 

The answer is 

A., d., and f i think