1. Solve $6 = \frac{a}{4} + 2$. Subtract 2 from both sides: $6 - 2 = \frac{a}{4}$. Simplify: $4 = \frac{a}{4}$. Multiply both sides by 4: $4 \times 4 = a$. Answer: $a = 16$. 2. Solve $-6 + \frac{x}{4} = -5$. Add 6 to both sides: $\frac{x}{4} = -5 + 6$. Simplify: $\frac{x}{4} = 1$. Multiply both sides by 4: $x = 4$. 3. Solve $9x - 7 = -7$. Add 7 to both sides: $9x = 0$. Divide both sides by 9: $x = 0$. 4. Solve $0 = 4 + \frac{n}{5}$. Subtract 4 from both sides: $-4 = \frac{n}{5}$. Multiply both sides by 5: $n = -20$. 5. Solve $-4 = \frac{r}{20} - 5$. Add 5 to both sides: $-4 + 5 = \frac{r}{20}$. Simplify: $1 = \frac{r}{20}$. Multiply both sides by 20: $r = 20$. 6. Solve $-1 = \frac{5 + x}{6}$. Multiply both sides by 6: $-6 = 5 + x$. Subtract 5 from both sides: $x = -11$. 7. Solve $\frac{v + 9}{3} = 8$. Multiply both sides by 3: $v + 9 = 24$. Subtract 9 from both sides: $v = 15$. 8. Solve $2(n + 5) = -2$. Divide both sides by 2: $n + 5 = -1$. Subtract 5 from both sides: $n = -6$. 9. Solve $-9x + 1 = -80$. Subtract 1 from both sides: $-9x = -81$. Divide both sides by -9: $x = 9$. 10. Solve $-6 = \frac{n}{2} - 10$. Add 10 to both sides: $4 = \frac{n}{2}$. Multiply both sides by 2: $n = 8$. 11. Solve $-2 = 2 + \frac{v}{4}$. Subtract 2 from both sides: $-4 = \frac{v}{4}$. Multiply both sides by 4: $v = -16$. 12. Solve $144 = -12(x + 5)$. Divide both sides by -12: $-12 = x + 5$. Subtract 5 from both sides: $x = -17$. Each problem uses the two-step equation solving method: isolate the variable term by undoing addition or subtraction, then undo multiplication or division to solve for the variable.