12. $-\frac{3}{5}x-\frac{7}{10}x+\frac{1}{2}x=-56$

Explanation:

Step1: Find a common denominator

The common denominator of 5, 10 and 2 is 10. Rewrite the left - hand side terms: $-\frac{3\times2}{5\times2}x-\frac{7}{10}x+\frac{1\times5}{2\times5}x=-56$, which simplifies to $-\frac{6}{10}x-\frac{7}{10}x+\frac{5}{10}x=-56$.

Step2: Combine like terms

$(-\frac{6 + 7-5}{10})x=-56$, so $(-\frac{8}{10})x=-56$, or $-\frac{4}{5}x=-56$.

Step3: Solve for x

Multiply both sides by $-\frac{5}{4}$: $x=-56\times(-\frac{5}{4})$. $x = 70$.

Answer:

$x = 70$