Answer (B) is correct . Overhead is applied on the basis of planned machine hours. The predetermined overhead application rate is $15 [($1,200,000 FOH + $2,400,000 VOH)/240,000 machine hours]. Thus, total overhead applied was $315,000 (21,000 planned machine hours based on output*$15).

Answer (A) is incorrect because The total overhead applied was $315,000 based on 21,000 hours at $15 per hour. Answer (C) is incorrect because The total overhead applied was $315,000 based on 21,000 hours at $15 per hour.
Answer (D) is incorrect because The amount of $300,000 is based on planned direct labor hours at $75 per hour.
Answer (C) is incorrect because The total overhead applied was $315,000 based on 21,000 hours at $15 per hour.
Answer (D) is incorrect because The amount of $300,000 is based on planned direct labor hours at $75 per hour.