#### Answer

Inverse action: turn the start key off.

#### Work Step by Step

In loose terms,
let f(unstarted car)=started car
We want the inverse to be defined on started cars,
g(started car)=unstarted car
So,
g(f ( unstarted car )=unstarted car
and
f(g( started car )=started car.
[ f(g(x))=x and g(f(x))=x ]
Inverse action: turn the start key off.