Hi aspirant

Total Mass ( Mass no.) = Total no. of protons + Total no. of neutrons (as the mass of electron is negligible hence not taken into consideration).

Now carbon has 6 neutrons and protons.

if the mass of protons is reduced by 2 times, that means no. of protons become 6/2 = 3

if the mass of neutrons is increased by 4 times, that means no. of neutrons become 6 x 4 = 24

hence the new mass no. will be 3 + 24 = 27