What is the missing number in the data set 15,17,28,30 if the mean is 23

Mean is add the numbers and divide the result by how many numbers there are

mean=23

1 missing number which is x

5 numbers including missing one

(15+17+28+30+x) / 5=23

solve for x

multiply both sides by 5

15+17+28+30+x=115

add like terms

90+x=115

subtract 90

x=25

the missing number is 25

15+17+28+30=90, if theres another number than there r 5 total numbers, 23*5=115, 115-90=25, so 25