Celia is scheduled to work a total of 20 hours this week. So far she has worked 75% of her hours. How many hours has she worked so far this week?

15 hours.

Step-by-step explanation:

20 can be divided into quarters, 3 quarters is 15/20 hours.

Your question is not clearly stated. Do you mean the difference between 10 * 10 * x, and 7 * 7 * 7 *x ? Then the number is x = 119/243. That's about 0.48971... in decimal form.

It's confusing when you say the "difference of a number". Differences are BETWEEN two numbers. See what I mean?