This is approx $400 in US dollars when comparing 460 Canadian dollars<span />
The decimal form for 5.63 x 10^-6 is 0.00000563
I personally use y2-y1 over x2-x1 because it's simple. Plot two y values and two x values. The first ones you plotted are x1 and y1, the others are x2 y2. Now subtract y2-y1 and x2-x1. Afterwards, divide the y value by the x value, that will give you slope.
The answer is 15% of $2.55=$0.3825=$0.38 off
Step by step: Take 15% and divide 15% by $2.55 This will give you the amount of money that is going to be added onto the bill. When you divide it and get your answer just add the answer to your original bill.