What’s the answer? Because I can’t find it out myself

Which matrix multiplication is possible?

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

Acar travels at an average speed of 52 miles per hour. how long does it take to travel 299 miles