Solving this problem resides in how the problem was stated in the first place.
The $20 tip shouldn't have been added onto the end of the equation, if anything,
it should have been subtracted. The $20 tip was already included in the $270 the
couples paid for the boat not the $30.00 that they pocketed. The $30 should have
been the amount added to the $270. $270 + $30 = $300