What is the value of this expression when t=-12

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

Angles r and s are complementary. the measure of angle r is 31 degrees. which equation can be used to find angle s?

Solve this problem! extra ! 3025/5.5 = a/90.75