Can someone help me please I really need help please

What is the length of the segment joining the points at (4,5) and (6,-2) round to the nearest tenth if necessary

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

Can someone answer this question? : )