here

E_n = -2.1 10-18 J/n² for H atom

Here n is the shell number
now you want to calculate for 5th shell so just plug in n= 5  --part (a )
Li²⁺ is hydrogen like atom and has more nuclear charge
E_n = -2.1 10-18 J Z²/n² for H like ions.

Plug in Z for Li ²⁺ = 3 and n = 3 in avove equation --Part 2

Bohrs Radius = 52.9 n²/Z  pm ----part 3
Now plug in n value as 5 and Z=1 (atomic number)