You got the following scores on 3
tests: 84, 82, 98. what score must
you get on the 4th test if you want to
average a 90% for the 4 tests?
a. 94
b. 95
c. 96
d. 97
e. 98

Your answer is c. 96
I know this because if you go on the calculator and add up 84+82+98+96 its equals to 360 and 360 divided by four (since there are now four marks including the mark you need to get on the next test) and that equals to 90. 

(in other terms)
84+82+98+96=360
360÷4=90
therefore, you need to get a score of 96 on your fourth test to receive an average of 90%

Well formatted version of question :

Olga tried to solve an equation step by step

1/4(1/3k+9)=6

step 1- 1/3k+9=24

step 2- 1/3k=15

step 3- k=5

find olgas mistake

step 1

step 2

step 3

olga did not make a mistake

Step 3

Step-by-step explanation:

Given the equation :

1/4(1/3k+9)=6

Step 1 : Olga multiplied both sides by 4

1/4(1/3k + 9) * 4 = 6* 4

1/3k + 9 = 24

Step 2 : Olga subtracted 9 from sides

1/3k + 9 - 9 = 24 - 9

1/3k = 15

Step 3 : Both sides should be multiplied by 3

1/3k * 3 = 15 * 3

k = 45

This is the step Olga made a mistake. Olga attempted to divide 15/3 = 5 instead of Multiplying 15 * 3 to obtain 45