In the Whisker-Box plot, the Lower Quartile can be found by the end of the left side of the box. In this case, it is directly above the -4, and so is your answer.
The tax is calculated by 0.075 * 21.25 = 1.59375 or $1.59. So the total bill is the cost of items purchased plus tax, which is $21.25 + $1.59 = $22.84.
