Subtract rational numbers: fractions with unlike denominators

Give the answer as a fraction in lowest terms, or a whole number.

1. Evaluate: −2/3 − 7/8 (Write a fraction in lowest terms, or a whole number.)
2. Evaluate: 2/3 − 1/3 (Write a fraction in lowest terms, or a whole number.)
3. Evaluate: −1/3 − 3/5 (Write a fraction in lowest terms, or a whole number.)
4. Evaluate: 2/3 − 2/3 (Write a fraction in lowest terms, or a whole number.)
5. Evaluate: 7/8 − (−1/6) (Write a fraction in lowest terms, or a whole number.)
6. Evaluate: 3/4 − 2/5 (Write a fraction in lowest terms, or a whole number.)
7. Evaluate: 1/2 − 2/3 (Write a fraction in lowest terms, or a whole number.)
8. Evaluate: 1/6 − 3/10 (Write a fraction in lowest terms, or a whole number.)
9. Evaluate: 9/10 − (−3/5) (Write a fraction in lowest terms, or a whole number.)
10. Evaluate: −1/2 − (−3/5) (Write a fraction in lowest terms, or a whole number.)
11. Evaluate: −2/3 − 3/4 (Write a fraction in lowest terms, or a whole number.)
12. Evaluate: −2/3 − 1/4 (Write a fraction in lowest terms, or a whole number.)
13. Evaluate: 4/9 − (−3/5) (Write a fraction in lowest terms, or a whole number.)
14. Evaluate: 1/4 − 1/8 (Write a fraction in lowest terms, or a whole number.)
15. Evaluate: −2/9 − (−1/2) (Write a fraction in lowest terms, or a whole number.)
16. Evaluate: 2/3 − 1/4 (Write a fraction in lowest terms, or a whole number.)
17. Evaluate: 1/2 − (−1/9) (Write a fraction in lowest terms, or a whole number.)
18. Evaluate: 3/8 − (−1/2) (Write a fraction in lowest terms, or a whole number.)
19. Evaluate: 7/8 − (−4/5) (Write a fraction in lowest terms, or a whole number.)
20. Evaluate: −1/4 − 1/2 (Write a fraction in lowest terms, or a whole number.)