Noun/adjective agreement

What this means is both the nouns/adjectives have to agree in gender, number, and case.

For example,

If we have the word ann__orum__, we must figure out the number, gender, and case.

If you know all of your declension you should look at the ending (orum) which should tell you that this is a genitive ending and that this is plural. And since this is also in the 2nd declension, the majority is masculine so now we know the gender.

Impius, Impia, Impium

Annorum 2nd(m) 1st(f) 2nd (n)

gen-plural-masc

Now at this point you should be able to pick one of the one's that are available (Impius, Impia, Impium)
 to be used in the sentence. (P.s it doesn't matter if the declension is completely different, you 
just have to get the same gender (in this case m) number (in this case plural) and case (in this case gen)

So the answer is…. Impiorum

One more example….

Lustus, Lusta, Lustum

Sacerdote

(remmember, first step is to figure out gender number case…)

abl - sing - masc

So the answer would be lusto.