Please help me with the question please ASAP ASAP

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

What are the coordinates of the midpoint of ab? ,1/2) /2,-1) ,-3/2) /2,-2)

How do you write something in scientific notation?