Erm, go and buy some screws and rawlplugs?

Better still, forget screws and rawlplugs and buy hammer in rawlbolts. This
way, you position the unit on the wall, drill a hole through the back
(through a strong section, not hardboard) typically at 10mm and then drill a
10mm hole into the masonry. The plug inserts and is hammered in, with a
final twist with a screwdriver. Drilling through the hole in the unit means
that the masonry hole doesn't wander and is in exactly the correct location.

Far easier than marking on the wall and drilling for rawlplugs, which will
be 5mm away from where you intended, at least with my drilling skills.

Christian.