PLEASE HELP FAST On Monday a group of students took a test and the average ( arithmetic mean ) score was exactly 80.4. A student who was absent on Monday took the same test on Tuesday and scored 90. The average age test score was then exactly 81. How many students took the test on Monday?
A) 14
B) 15
C) 16
D) 17
E) 18
With steps please

Regressive taxation has one of the most criticised forms of taxation due to its burden on people who are less fortunate to pay. By definition, a regressive tax is " a tax imposed in such a manner that the tax rate decreases as the amount subject to taxation increases" as defined by Wikipedia. It is directly proportionate to the income that the person earns.