It took us . . . . . . . . hour and . . . . . . . . half to do shopping and we got . . . . . . . . home at 4.

In the first blank, article "an" will be used because 'hour' starts with a vowel sound.
Similarly, in the second blank, article "a" will be used because article "a" is used when the speaker is making a general statement and the noun is having a consonant sound.
In the third blank, "no article" or "zero article" because 'no article' is preceded when preposition like 'of' or 'at' is used.