The atomic mass of lithium-6 is 6.015123 u. how much energy is required to completely separate the nucleons in a lithium-6 nucleus?

What is asked is the binding energy. The formula is

E = c² Δm

In a lithium-6 atom, there are 3 protons and 3 neutrons.

The mass of the nucleus is

3 (1.672622) + 3 (1.674927) = 10.035344

The binding energy is

E = (3x108) ² (10.035344 - 6.015123)

E = 3.618 x 10^17 J