Can someone please answer these for me?

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

Find the domain of the following expression: 1/(√x)-2

Write the expression 7x^3-28xy^2 as the product of 3 factors