she saved $3, and we know the discount is 15%, so her savings is that 15%, thus we know 15% of that purchase is 3.
let's say the full price is x, and therefore the 100%, if we know 3 is the 15%, what is x?

The choices are in the slope-intecept form: y = mx + b, where m is the slope and b is the y-intercept. Looking at the graph, the y-intercept is the point at which it intersects the y-axis. That would be -1. So, the answer is either the 1st or 2nd choice. Next, we find the slope. Take 2 points that lie along the line. For example, points (1,2) and (2,5). Calculate for the slope.
m = (y2-y1)/(x2-x1)
m = (5-2)/(2-1)
m = 3
Hence, the graph is y = 3x - 1
Tan=24/10 ≈ 2.4
using Pythagoras theorem
x²=(24)²+(10)²
x²=576+100
x²=57600
x=√57600 => 240
Therefore
sina=24/240 => 0.1
cota=1/tana => 1/(24/10) => 10/24