If f(x) = 10x -16. What is the value of (6)?

Really need on these. i have no idea what to do

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

A50% increase followed by 33 1/2% decrease