You have already learnt how to use the genitive with fourth declension nouns (the ones whose endings don't change). See Exercise 8.8 if you are not sure.

All nouns in the first declension are masculine and end in a broad consonant. To form the genitive, you make the ending slender (by inserting an i before it). But note also:
* ea is changed to i
* éa is changed to éi

The other thing to remember is that masculine nouns in the genitive are aspirated after the article; but you cannot aspirate nouns beginning with d or t.

To complete this exercise, rewrite the words in brackets using the genitive where required.