1. Simplify the expression: $3(-7)^2 = \_\_\_$.
2. Evaluate the expression $3 - x^2$ for $x = -4$. The value is ___.
3. Evaluate $\frac{3b^3}{6} - \frac{4 - a^2}{8}$ for $a = 6$ and $b = -2$. The result is ___.
4. Solve the formula $A = \frac{h}{2}(b + c)$ for the variable $c$.
5. Simplify the expression: $\sqrt{13^2 - 5^2} = \_\_\_$.
6. Evaluate the expression $m^3 + n^3$ for $m = 3$ and $n = 2$. The value is ___.
7. Evaluate the expression $(m + n)(m^2 - mn + n^2)$ for $m = 3$ and $n = 2$. The value is ___.
8. Evaluate $\sqrt{x^3 + y^3 + z^3}$ for $x=3, y=4, z=5$. Round to three decimal places. The value is ___.
9. Solve the formula $S = \frac{n}{2}(a + f)$ for the variable $a$.