What are the steps to solving this equation: ( 3a^4) ( -6a^3)

The answer is c because you turn 17.5% into a decimal which gives you .175 then you times that by $361.35 which gives you 63.23625 but then you round that which gives you 63.24. then you at 63.24 pulse 361.35 and you round it which gives you $425

21 is the answer the answer is 21