Open the Screen Shot and Help me Please

What is the point-slope equation of a line with slope -5 that contains the point (6,3)

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

Any is very appreciated! (picture is provided below)not sure how to do this at all won't lie