Respuesta :

you can think the third score is x
86+85+x=90*3
x=99
cchikoo
3*90=270 ( multiply the number of tests which is 3, times 90 to get the total score)

86+85=171 (adding two test together)
270-171= 99

You will need at least 99 in your third test!

Hope this helps!