Question 1141369
(a+b)/2=z
so 2z=a+b
the average of a, b, and I presume c, not d, is (a+b+c)/3
This is (2z+c)/3
D

Let a=8 b=4 and c=6.  2z=12
average of and b is 6 and average of all 3 is 6
(2z+c)/3=6