PLEASE PLEASE PLEASE HELP ME

Which equation can be used to solve for the unknown number? seven less than a number is thirteen. n-7=13 7-n=13 n+7=13 n+13=7

How can you decide witch operations to use to slice a two step equation

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?