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?
A) m+6 B) m+7 C) 2m+14 D) 3m+21
First write x, y, and z in terms of m
hint: z=(3m+18)/2
then add x, y, and z together and divide by 3. (because there are 3 of them)
Now you do it
+15 
