Help asp plz I don’t get it soo yea

What number must you add to complete the square x^2+12x=16

On the april 3 billing date, michaelle chappell had a balance due of $ 1495.39 on her credit card. from april 3 through may 2, michaelle charged an additional $ 305.34 and made a payment of $ 800.a) find the finance charge on may 3, using the previous balance method. assume that the interest rate is 1.8 % per month.b) find the new balance on may 3.

Solve for n? [tex]z = \frac{3}{4} mn[/tex]