A) The information that is not needed to compute the total cost after tax and tip is the tax percentage, 7%. This is because the 15% includes the tax and tip.
B) Tax and tip are always added on top of an amount. Our equation can be set up as such: 15% of the bill (including tax, not including the tip) = the tip
15% = 0.15 as a decimal
of = multiplication
cost (excluding tip) = x
tip = 1.05
0.15(x) = 1.05
x = 7
Remember that x is just the cost, and does not include the tip. Therefore, we need to add the tip back in.
7 + 1.05 = 8.05
Total Bill = $8.05
Hope this helps!