Ella’s test grades in her history class are 89, 94, 82, 84, and 98. what score must ella make on her next test to have a mean test score of 90?

Mean is same as average

to find average
add up terms
divided that sum by the number of terms you have
example

mean of x,y,z
x+y+z
3 terms
(x+y+z)/3=mean

so
represent next test score as x
89+94+82+84+98+x
count how many terms ther are (6 terms)

mean is 90
(89+94+82+84+98+x)/6=90
add the like terms
(447+x)/6=90
multiply both sides by 6 to clear fraction
447+x=540
subtract 447 from both sides
x=93

she needs a score of 93 on next test