Half of a number decreased by 8 is 3

With the help you've gotten in the last 15 minutes or so,
you should be able to do this one now.

The mystery number . . . . . . .      M
Half of it . . . . . . . . . . . . . . . .  1/2 M
Half of it decreased by  8 . . .  1/2 M - 8

You said that's  3 .
So the equation you have to solve is

                                      1/2 M - 8  =  3

Add  8  to each side:      1/2 M       =  11

Multiply each side by  2 :      M       =  22

This is easier than the last one we ( I ) did.    

The right answers for the question are