To simplify the expression $\frac{2}{5} + \frac{7}{3} - \frac{9}{4}$, we need to find a common denominator. The denominators are 5, 3, and 4. The least common denominator (LCD) of these numbers is 60.

1. Rewrite each fraction with a denominator of 60: $\frac{2}{5} = \frac{24}{60}, \quad \frac{7}{3} = \frac{140}{60}, \quad \frac{9}{4} = \frac{135}{60}$

2. Now, combine the fractions: $\frac{24}{60} + \frac{140}{60} - \frac{135}{60} = \frac{24 + 140 - 135}{60} = \frac{29}{60}$

So, the simplified result is: $\frac{29}{60}$

Would you like further details or have any questions?

Here are some related questions:

1. How do you find the least common denominator?
2. What are the steps to simplify complex fractions?
3. How do you convert improper fractions to mixed numbers?
4. How can you add fractions with different denominators?
5. What is the difference between rational numbers and fractions?

Tip: When adding or subtracting fractions, always look for the least common denominator to make the process easier!