Solving equations and distributive property

4. find the geometric mean of 4 and 12. 24 8

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

If a || b and b | y, then ? a) x || y. b) x | a. c) a | y. d) a || y.