Answer:
The correct answer is Option C.
Step-by-step explanation:
1) Simplify 9/60 to 3/20.

2) Simplify x/24 - x/30 to x/120.

3) Multiply both sides by 120.

4) Use this rule: a/b × c = ac/b.

5) Simplify 3 × 120 to 360.

6) Simplify 360/20 to 18.

Therefor, the answer is option C. 18.