I got 6 out of 14 wrong on a test what would that do to my average of an 90

Question

So I got 6 out of 14on a test but my math average is a 90 so how low would my grade go?

Answer 1

6/14 = 3/7 and 4/7 right = about 57.1

if this is the 3rd test add 2(90) to 57.1, then divide by 3 to get a new average of 79.0

if this is the 10th test then add 9(90) + 57.1, then divide by 10 to get a new average of 86.7

in general

if there are N tests used in the average then the new average = (90N+57.1)/N. where the new average could be anywhere between 79 to 86.7 if 2<N<11