Answer: These are the correct answers:
1. Cuarenta y una.
2. Mil.
3. Doscientas cincuenta y nueve.
4. Dos millones de.
5. Treinta y un.
6. Cien
Explanation: Just to elaborate a little on the answer, it can be added that in this exercise they are asking you to use the correct form of the cardinal numbers. Some cardinal numbers in Spanish (twenty-one, thirty-one, and so on) must agree with the gender of the word. Since "chicas" and "fotografías" are feminine, you must say "cuarenta y una" and "doscientas cincuenta y nueve." In addition, the word "miles" means thousands and the word "cientos" mean hundreds, and, like in English, if they are followed by a noun they must have the preposition of ("de" in Spanish). The cardinal numbers twenty-one, thirty-one, and so on in Spanish can be "apocopados," this is to know, shortened (you say "treinta y un chicos" or "treinta y uno").