Sara wants to buy a necklace. the necklace has a list pice of $41 and the saels tax is 6%what will be the cost of the necklace after tax is added

Ok, so because the necklace is $41 before the 6% sales tax is added, I would suggest that, first, you convert the percentage into a decimal.  To do that, I used to make the percent into a dot before moving the dot two spaces to the right.
(6% > 0.06)
Then, I would suggest that you use a trick I learned when dealing with problems like these; add 1 to your new decimal.  This makes it so that your original amount remains while also adding your sales tax.
(0.06+1=1.06)
Then multiply!
41 * 1.06 = 43.46

The vertex of the quadratic function is (1.5, -.75)