If x is the average (arithmetic mean) of m and 9, y is the average of 2m and 15, and z is the average of 3m and 18, what is the average of x, y, and z in terms of m?
I will assume that 2m means one number 2m and NOT m + m and 3m does not mean three m's
x = (m+9)/2 y = (2m+15)/2 z = (3m+18)/2
To find their average, add them together and divide by 3
[ (m+9)/2 + (2m+15)/2 + (3m+18)/2 ] / 3
(6m + 42)/2 / 3
3m+21 / 3