$($ I want step by step solution only with proper explanation and solving of each and every step at constant volume only $)$ Derive the following equations using Maxwell relations:

$($a$)U=F-T(\frac{\text{d}\text{e}\text{l}\text{F}}{\text{d}\text{e}\text{l}\text{T}}{)}_V$

$($b$)H=G-T(\frac{\text{d}\text{e}\text{l}\text{G}}{\text{d}\text{e}\text{l}\text{T}}{)}_V$