X^2 - 7x + 12 = 0
x^2 - 4x - 3x + 12 = 0
x (x - 4) -3 ( x - 4) = 0
(x - 4) (x - 3) = 0
x = 3 , 4
Check the answer by plugging in 3 and 4 for x, if the equation equals zero then you have your answer.
In all right triangles, the ratio between a leg and the hypothenuse is the sine of the angle opposite to the leg.
So, in your case, we have

In order to find XY, we have

So, the ratio for the sine is

Let's start by understanding that the graph is a linear line. We have a common difference if 4.5 for every 10x we have more.
We can start by finding the gradient, using rise over run. Let's take (10, 4.5) and (20, 9)
Our rise is 9 - 4.5 = 4.5 and our run is 10. Then, our gradient becomes 4.5/10 = 0.45
Now, we can substitute points using the point-slope form.
y - 4.5 = 0.45(x - 10)
y - 4.5 = 0.45x - 4.5
Hence, our line becomes y = 0.45x and you can verify by substituting in points from the table.