Solve for x: a) x + 3 + 2 = 4, b) x + 8 + 7 = -8, c) x + 6 + 6 = 3, d) x - 9 - 8 = -3, e) x − 5 − 4 = 7, f) x - 11 + 5 = -7

$$x + 3 + 2 = 4$$ $$x + 5 = 4$$

$$x + 5 - 5 = 4 - 5$$ $$x = -1$$

The solution is $\boxed{x = -1}$.

b)

$$x + 8 + 7 = -8$$ $$x + 15 = -8$$

$$x + 15 - 15 = -8 - 15$$ $$x = -23$$

The solution is $\boxed{x = -23}$.

c)

$$x + 6 + 6 = 3$$ $$x + 12 = 3$$

$$x + 12 - 12 = 3 - 12$$ $$x = -9$$

The solution is $\boxed{x = -9}$.

d)

$$x - 9 - 8 = -3$$ $$x - 17 = -3$$

$$x - 17 + 17 = -3 + 17$$ $$x = 14$$

The solution is $\boxed{x = 14}$.

e)

$$x - 5 - 4 = 7$$ $$x - 9 = 7$$

$$x - 9 + 9 = 7 + 9$$ $$x = 16$$

The solution is $\boxed{x = 16}$.

f)

$$x - 11 + 5 = -7$$ $$x - 6 = -7$$

$$x - 6 + 6 = -7 + 6$$ $$x = -1$$

The solution is $\boxed{x = -1}$.

4. Solve for $x$:

a)

$$3x = 27$$ $$\frac{3x}{3} = \frac{27}{3}$$ $$x = 9$$

The solution is $\boxed{x = 9}$.

b)

$$5x + x = 18$$ $$6x = 18$$

$$\frac{6x}{6} = \frac{18}{6}$$ $$x = 3$$

The solution is $\boxed{x = 3}$.

c)

$$2x - 4 = 10$$ $$2x - 4 + 4 = 10 + 4$$ $$2x = 14$$

$$\frac{2x}{2} = \frac{14}{2}$$ $$x = 7$$

The solution is $\boxed{x = 7}$.

d)

$$7x = 28$$ $$\frac{7x}{7} = \frac{28}{7}$$ $$x = 4$$

The solution is $\boxed{x = 4}$.

e)

$$5m = 25$$ $$\frac{5m}{5} = \frac{25}{5}$$ $$m = 5$$

The solution is $\boxed{m = 5}$.

f)

$$15ab = 30$$ $$\frac{15ab}{15} = \frac{30}{15}$$ $$ab = 2$$

The solution is $\boxed{ab = 2}$.

5. Solve for $x$:

a)

$$\frac{4x}{6} = 12$$ $$6 \times \frac{4x}{6} = 12 \times 6$$ $$4x = 72$$

$$\frac{4x}{4} = \frac{72}{4}$$ $$x = 18$$

The solution is $\boxed{x = 18}$.

b)

$$\frac{x}{5} = 15$$ $$5 \times \frac{x}{5} = 15 \times 5$$ $$x = 75$$

The solution is $\boxed{x = 75}$.

c)

$$\frac{x}{2} = 30$$ $$2 \times \frac{x}{2} = 30 \times 2$$ $$x = 60$$

The solution is $\boxed{x = 60}$.

d)

$$\frac{x}{3} = 6$$ $$3 \times \frac{x}{3} = 6 \times 3$$ $$x = 18$$

The solution is $\boxed{x = 18}$.

e)

$$\frac{x}{3} = 24$$ $$3 \times \frac{x}{3} = 24 \times 3$$ $$x = 72$$

The solution is $\boxed{x = 72}$.

f)

$$\frac{x}{7} = 7$$ $$7 \times \frac{x}{7} = 7 \times 7$$ $$x = 49$$

The solution is $\boxed{x = 49}$.

Problem solving:

"a divided by 25 equals 100" can be written as:

$$\frac{a}{25} = 100$$

$$25 \times \frac{a}{25} = 100 \times 25$$ $$a = 2500$$

The solution is $\boxed{a = 2500}$.