Official solution
Let,
p : n3--1 is even,
q : n is odd
Contrapositive of p \[ \to \] q = \[ \sim \]q \[ \to \] \[ \sim \]p
\[ \Rightarrow \] If n is not odd then n3 -- 1 is not even.
\[ \Rightarrow \] For an integer n, if n is even, then n3 -- 1 is odd.