Answer:
c 18
Step-by-step explanation:
Idid thsi in Kahn academy and got it correctly
First set everything to 0.

Giving you A= 1 , B= 1 and C= -5
Then input everything into the quadratic formula and either solve by hand or use a calculator.
Note exact values are found by hand, decimals are found using a calculator.
1200 - 450 = 750 liters that he needs to fill up
81.5 x 750 = €61,125
€61,125 x 0.075 = €4,584.38 (discount as a loyal customer)
total paid with discount = €61,125 - €4,584.38 = €56,540.62
answer
Mr. Leonard gets €4,584.38 discount on his purchase