SOMEONE PLEASE HELP ME ASAP 15 POINTS

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

Atriangle with all sides of equal length is a/an triangle. a. right b. scalene c. equilateral d. isosceles

Hi, can anyone show me how to do this problem? 100 points for this. in advance