Final answer:
In the sentence, the word 'work' should be in the past simple tense, resulting in 'worked'. The sentence should read: 'Janet worked for Smith and Brothers before she came to work for us.'
Step-by-step explanation:
The sentence provided is an example of a context where we need to use the past simple tense, to express an action completed in the past. The verb being used here is 'work'. To use this verb in the past simple tense for the subject 'Janet', we need to add 'ed' at the end, because 'work' is a regular verb. However, 'work' is also an exception where the 'ed' ending is pronounced as /t/ and not as /d/ or /ed/. With this in mind, the sentence should be completed as: 'Janet worked for Smith and Brothers before she came to work for us.'
Learn more about Past Simple Tense