Final answer:
The corrected sentence should read: 'Sergei stood and said, "Assuming our forecast for next quarter is correct, all of you can expect a sizable bonus." The comma after 'said' introduces the direct quote and the quote is enclosed within quotation marks. The question mark is replaced with a period.
Step-by-step explanation:
The re-punctuated sentence should read: 'Sergei stood and said, "Assuming our forecast for next quarter is correct, all of you can expect a sizable bonus."' In this corrected sentence, a comma is used after 'said' as it is introducing a direct quote. The entire spoken portion is enclosed within quotation marks. The question mark is replaced with a period because the statement is not formulated as a question.
In terms of rules, the first word of a direct quote (Assuming) should be capitalized if it's a complete sentence. If you were to leave the original phrasing, the word 'expect' would have to stand in place of 'can expect' to make the sentence grammatically correct.
Learn more about Punctuation Correctness