Official solution
Given,
(p \[\vee\] q) \[\Rightarrow\] ((\[\sim\] r) \[\vee\] p)
Negation is
\[\sim\] ((p \[\vee\] q) \[\Rightarrow\] (\[\sim\] r) \[\vee\] p))
= (p \[\vee\] q) \[\wedge\] \[\sim\] ((\[\sim\] r) \[\vee\] p)
= (p \[\vee\] q) \[\wedge\] (r \[\wedge\] \[\sim\] p)
[(p \[\wedge\] \[\sim\] p) \[\vee\] (q \[\wedge\] \[\sim\] p)] \[\wedge\] r
= q \[\wedge\] \[\sim\] p \[\wedge\] r