Step-by-step explanation:
We have
87+86+x
T is the total scores
n is number of tests done = 3
T/n is greater than or equal to 90
To get minimum test
T/n = 90
T = 90*n
= 90n
We solve for x
Remember n = 3
90x3 = 270
270 = 87+86+x
270 = 173+x
X = 270-173
X = 97
1.
X = 97
2.
You didn't add a value in your part b question. I used 80 though.
T/n < 80
T<80n
80x3= 240
T<240
87+86+x<240
X<240-173
X<67
X has to be less than 67 so we conclude that if x <=67 b grade will be lost.