Answer: These are the right answers:
1. leerían
2. decidirías
3. decidiríamos
4. sabría
Explanation: Just to elaborate a little on the answer, it can be added that in this exercise they are asking you to choose the correct form of the verb, according to the subject. The verbs are conjugated in the so-called "condicional simple" (simple conditional). So, for instance, in sentence 1, since the subject is "ustedes" (you plural), the right form of the verb is "leerían." You can translate that sentence as "You would read the history of Cartagena."
