Can I please get some additional help on #6?

Marla bought a book for $12.95, a binder for $3.49, and a backpack for $44.99. the sales tax rate is 6%. find the amount of tax and the total she paid for these items

The interior angles formed by the side of a hexagon have measures of them up to 720° what is the measure of angle a

What is the point of inflection for the function f(x)=2cos4x on the interval (0, pi/2)