Please help with question below​

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

Two times a number plus three times another number equals 4. three times the first number plus four times the other number is 7. find the numbers

You earn a 12% commission for every car you sell. how much is your commission if you sell a $23,000 car?