Let x be the total amount collected at the door. Then, we can write
where the 0.02 denotes the comission of 2%. From this equation, we can find x.
Then, by moving 3000 to the right hand side, we have
which gives
Now, by moving 0.02 to the right hand side, we get
then, x is given by
Therefore, the total amount collected at the door is $ 27 000.