Always always always where MC=MR
With your givens, I must assume that MC=AVC=20 at one PARTICULAR PRODUCTION LEVEL, and MC=ATC=30 at another PARTICULAR PRODUCTION LEVEL. Both statements cannot be true at the same production. So, I presume that the firm has a normal increasing marginal cost function. Further, it must be that for production above this particular level, MC=AVC at the minimum point of the AVC curve. So, at points to the right of this point, MC must be greater than AVC. Also, MC=ATC at the minimum point of the ATC curve.
Hint: a picture would be very helpful. Draw a firm with MC,AVC, and ATC curves, the MC curve cuts the AVC and ATC curves at their minimum point.
Since the firm is in a perfectly competitive market, MR=average revenue=Price -- for all levels of output. So....
A) produce where MC=MR -- and increase in production
B) P=25
C) Yes as MR > AVC, the firm is at least covering its variable costs.
D) No, at MR=25, MR < ATC -- the running at a loss.