Teacher:You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.
Teacher: Now, understand the problem? Solve this instance: Question: An eccentric casino owner decides that his casino should only use chips in $3 and $7 denominations. Which of the following amount cannot be paid out using these chips?

Option A: $27

Option B: $24

Option C: $23

Option D: $25

Option E: $21
Student:
Option D