If the mean and the variance of the numbers $a, b, \mathrm{8,} 5$ and $10$ are $6$ and $6.8$ respectively, then the value of $a^3+b^3$ is equal to

• A

  $58$
• B

  $61$
• Correct answer
  C

  $91$
• D

  $89$

Hence, the correct answer is option: 'C'.