Assuming the experimental mass of ^ 12 _ 6 C as 12 u , the mass...

The mass of $6$ protons is $6 \times 1.00727\text{ u} = 6.04362\text{ u}$.

The mass of $6$ neutrons is $6 \times 1.00866\text{ u} = 6.05196\text{ u}$.

Total mass of the constituent nucleons is $6.04362\text{ u} + 6.05196\text{ u} = 12.09558\text{ u}$.

The mass defect $\Delta m$ is the difference between the total mass of the nucleons and the experimental mass of the atom (ignoring electron mass as per the given data):

$\Delta m = 12.09558\text{ u} - 12\text{ u} = 0.09558\text{ u}$

Converting the mass defect into $\text{MeV}/c^2$:

$\Delta m = 0.09558 \times 931.5\text{ MeV}/c^2 = 89.03277\text{ MeV}/c^2 \approx 89.03\text{ MeV}/c^2$

Answer: $89.03$