Question

change they shouted at the naughty boy" into passive voice

Answer 1

The correct passive voice of the given sentence is as shown below:

The naughty boy was shouted at by them.

Explanation

The active voice of the given sentence was in Simple Past Tense. So the passive voice of Simple Past Tense is 'was/were+V3 (Past Participle). When we convert an active voice sentence into passive voice sentence, the subject becomes object and vice versa.  

Answer 2

The naughty boy was shouted at by them.

While rewriting an active sentence into a passive sentence the object of the active sentence becomes the subject of the passive sentence.

In passive voice interest is shown in the person or object which experiences an action instead of the person or object which performs the action.