You can see that the first situation in the
list matches Robby's current situation.

It instructs him to move north, 
so now he would move one square north.

And then the second situation on the list,
which corresponds to his new situation--

you can see that--and the action
is pick up can, but he's in an empty space.

So when he picks up the can on 
an empty site, he gets minus one.

So this was the correct answer.