What is the average (arithmetic mean) of $6x^2+3x-8, \; 3x^2+2x-2$ and $3x^2+3$ ?

Question

$\begin{array}{1 1} (a)\;4x^2 - \frac{5}{3} x+ \frac{7}{3} \\ (b)\; 4x^2+\frac{5}{3}x-\frac{7}{3} \\ (c)\; 4x^2 -\frac{5}{3}x-\frac{7}{3} \\ (d)\; 4x^2+\frac{5}{3}x+\frac{7}{3} \end{array}$