Find the sales tax,, selling price: $40, rate of sales tax: 4%

Chanelle deposits $7,500 into the bank. she does not withdraw or deposit money for 6 years. she earns 6% interest during that time. what will the balance be when she is finally able to withdraw her money?

When i add money am i supposed to make it like this 7+12 or 7.00+12.00 because i got 19 dollars for my answer

2.5 milligrams is equivalent to how many grams