In Heidi's history class, the only grades that count toward the semester average are the 6 tests she has already taken and the upcoming final exam. The final exam counts as two tests. Heidi has determined that if she earns 99 points on the final she will have exactly a 90-point average for the semester. On average, how many points has Heidi scored on each test prior to the final exam?

87 points

Step-by-step explanation:

lets take "x" as the avg test scores of the past 6 tests

so

since their are 6 tests, we would represent the 6 tests as "6x"

to find average we need to add all numbers, and divide by the number of numbers

so since the final exam counts as two tests we need to add "99" twice

so

(6x+99+99)/8=90

multiply by "8" on bots sides and add 99 and 99 together

6x+198=720

subtract 198

6x=522

divide by 6

x=87

hope this helps