Given the slope m and a point (a,b) of a line, its equation is given by

In your case, a = -4, b = 7 and m=1/2, so we have

Answer:
D. 21 ft
Step-by-step explanation:
We need to use Power of Points, which basically says that for intersecting chords in a circle (see attachment), a * b = c * d.
Here, we can say that a = x, b = 6, c = 7, and d = 18. Then, we have the equation:
ab = cd
x * 6 = 7 * 18
6x = 126
x = 21
Thus, x is 21 ft.
Hope this helps!
4/5 is the slope. When you isolate the y on one side of a linear equation, whatever number is with the x value is your slope.
This is because simplifying the equation before solving it will lead you to the answer at a much faster rate. For example, in the given equation, the long way would be to distribute 2 to (x+3). Then, you transpose them and combine like terms. Until you get to x + 3 = 8. But if you simplify it first, you will see that it is straightforward. It will lead you to the answer right away which is x + 3 = 8. It saves you from the hassle of doing more algebra :)
Slope intercept form is y=mx+b. In this case, I believe it's y= -5/6x -5/6.