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Choose the correct classification of 3x4 − 9x3 − 3x2 + 6. 5th degree polynomial 4th degree polynomial 9th degree polynomial 24th degree polynomial

For the rule of 78, for a 12-month period, the last term in the sequence is 12 and the series sums to 78. for an 10 month period, the last term is and the series sum is . for a 15 month period, the last term is and the series sum is . for a 20 month period, the last term is and the series sum is

How do you use the elimination method for this question? explain, because i really want to understand!