The exterior dimensions of a saef are 90 cm x 50 cm x 30 cm. if the walls of the safe are 1.5 cm thick, what is the interior volume of that safe?

My guess:

Subtract 1.5 cm from 90 cm and from 50 cm and from 30 cm.

Then multiply to find the volume:
(90 - 1.5)(50 - 1.5)(30 - 1.5) = ?? cm

If I'm wrong, another teacher will correct me.

=)