Algebra=pain, Plz help lol

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

Which equation represents the function on the graph?

{0,1,2,3,4,5,6,20,21,22,23,24,25} the distribution is considered to be: skewed the right, skewed the left, not skewed?