I see that you've uploaded a math problem set. Let’s go through each of these problems one by one and solve them:

1) Solve: $3x - 12x - 4x + x$

Simplify the expression:

$3x - 12x - 4x + x = (3 - 12 - 4 + 1)x = -12x$

So, the solution is:

$-12x$

2) Solve: $\frac{x}{-7} = -8$

To isolate $x$, multiply both sides by $-7$:

$x = -8 \times (-7) = 56$

3) Solve: $\frac{4}{x} = 12$

Multiply both sides by $x$:

$4 = 12x$

Now divide by 12:

$x = \frac{4}{12} = \frac{1}{3}$

4) Solve: $\frac{1}{2}x + \frac{3}{5}x = 18$

Find a common denominator for the fractions. The common denominator of 2 and 5 is 10. Rewrite the equation:

$\frac{5}{10}x + \frac{6}{10}x = 18$

Now combine the terms:

$\frac{11}{10}x = 18$

Multiply both sides by 10:

$11x = 180$

Now divide by 11:

$x = \frac{180}{11} \approx 16.36$

Would you like further details on any of the steps, or have questions about any of the solutions?

Here are 5 related questions to consider for more practice:

1. Solve $5x - 3x + 7x - x$.
2. Solve $\frac{y}{-9} = 6$.
3. Solve $\frac{5}{x} = 15$.
4. Solve $\frac{2}{3}y + \frac{5}{6}y = 20$.
5. What is the value of $x$ in the equation $7x - 14 = 0$?

Tip: When working with equations that involve fractions, finding a common denominator can help simplify your work!