You can get rid of the fractions by multiplying through by the lowest common denominator (LCD).
Or, you can leave the fractions in and simplify the equation. For example:
-3x/7-2x/9 simplifies to -27x/63-14x/63=-41x/63.
-41x/63=-41/12, divide both sides by -41:
x/63=1/12, x=63/12=21/4.