I honestly don't even know where to start on his last 4 tests , Danilo scored 55% 78% 84% and 93%. What score should he get on the next test so that his average on all five tests is 80%?

The answer to your question is He must get 80%

Step-by-step explanation:

Data

Scores 55%, 78%, 84%, 93% and X

Average 80%

Process

1.- Write a equation to solve this problem

- There are five scores

Score 1 = S1 = 55

Score 2 = S2 =  78

Score 3 = S3 = 84

Score 4 = S4 = 93

Score 5 = S5 = X

Equation

               Average = (S1 + S2 + S3 + S4 + S5) / 5

- Solve for S5

               5 Average = S1 + S2 + S3 + S4 + S5

               S5 = 5 Average - S1 - S2 - S3 - S4

- Substitution

               S5 = 5(80) - 55 - 78 - 84 - 93

- Simplification

               S5 = 400 - 310

- Result

               S5 = 90