How to estimate 586-321 in two different ways

Which expression is equivalent to (3^2)^-2 a.-81 b.-12 c.1/81 d.1/12

A) if $50000 is invested in a bank account that pays 9.3% of interest compounded on a six-monthly basis, how much money will be in the account after 3 and 12 years? b) if matusalen's father had put $2.0 in the bank when he was born and there, how long would matusalen have had to his death (969 years later) if the interest was 7% per year composed each month and weekly?

Write numerical coefficient of y² in the expression 2x² - 15xy – 7y²