Justin couldn’t understand why his friend had refused to work in a company that offered him a huge salary.
If it had been him in his friend’s place, he would definitely accepted such an offer.

The given sentence follows the conditional type 3 sentence structure. Conditional sentences are given as: If + (conditional clause) , (main clause)

In the case of a type 3 conditional sentence, the conditional clause is in past perfect tense (subject + had + V3), while the main clause follows a perfect conditional or perfect continuous conditional (would have + V3); where V3 is the past participle form of the verb. 

In the given sentence : ...If it had been him in his friend’s place, he would definitely accepted such an offer. "

The clause "...If it had been him in his friend’s place" is the conditional, and hence the main clause should be he WOULD HAVE DEFINITELY ACCEPTED such an offer .

The correct answer is therefore option B.