Let the function $g$ be defined by $g(x)=5x+2$. If $\sqrt{g\left(\frac{a}{2}\right)}$, what is the value of $a$ ?

This may look complicated, but just follow the directions. You know that $g(x)=$ $5x+2$. You also know that $\sqrt{g\left(\frac{a}{2}\right)}=6$. First, get rid of the square root by squaring both sides. Now you have $g\left(\frac{a}{2}\right)=36$. Usually there's an $x$ inside the parentheses. Treat this the same. This statement says that $g$ of some number equals 6. You also know that $g$ of some number is the same as $5x+2$. So $5x+2$ $=$ 36. Simplify and you get $\frac{34}{5}$. Be careful here; you're not done. You now know that $\frac{a}{2}=\frac{34}{5}$, so $a=\frac{68}{5}$, or $(\mathrm{D})$