Answer:
1. difícil
2. muchos
3. atléticas
4. joven
5. grande
6. trabajadores
7. optimistas
8. morenos
9. perezoso
Step-by-step explanation:
In many cases (not all), when the noun is feminine, your adjective should end with an 'a' and when it is masculine, your noun should end with an 'o'
Of course, there are special cases when these rules do not apply
When your noun is talking about more than one thing, your adjective should be plural.