Stan took Lily to his friend's restaurant on a date. The friend told the waiter to remove the $12 dessert from Stan's bill. Stan tipped the waiter 20% on the reduced bill, which was a $15 tip. Fill in the blanks to write an equation that will determine the amount of the original bill, b.
The original bill, b, minus 12 dollars equals the reduced bill, b - 12 dollars.
Stan tipped the waiter 20% of the reduced bill, which equals (b - 12 dollars) * 20%.
This tip amount equals 15 dollars.
Writing down the equation we get: (b - 12 dollars) * 20% = 15 dollars. Answer: \boxed{\frac{b-12}{5}=15}.