Official solution
Let p denotes statement
p : I reach the station in time.
q : I will catch the train.
Contrapositive of p \[ \to \] q
is \[ \sim \]q \[ \to \] \[ \sim \]p
\[ \sim \]q \[ \to \] \[ \sim \]p : If I will not catch the train, then I do not reach the station in time.