D − 21.4 = 87 . Help! What is D?

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 sums are equal to 1hold 6/8? choose all answers that are correcta.1/8+6/8b.12/8+2/8c.8/8+1/8+1/8+1/8+1/8+1/8+1/8d.8/8+6/8

Plz ( true - false) all triangles have interior angles whose measure sum to 90.