Final answer:
To complete the sentence in future progressive tense, it should read 'Vangie will be volunteering for the Sunday School a week from now.'
Step-by-step explanation:
The sentence 'Vangie ----------- (volunteer) for the Sunday School a week from now' should be completed using the progressive tense. To denote an action that will be ongoing at a future time, we use the future progressive tense. The future progressive tense is formed with will + be + the present participle (verb-ing). The correct completion of this sentence is 'Vangie will be volunteering for the Sunday School a week from now'.