We want to find F U G, since the universal set is defined as such.
We can't directly add n(F) + n(G) since that would include duplicates from F and G, therefore we subtract by n(F ⋂ G), since n(F ⋂ G) gives what F and G share in common, removing the so called duplicate.
Therefore, Universal Set = n(F U G) = n(F) + n(G) - n(F ⋂ G) = 97+79-22=154 which is the option C.
