For any given y value, there can only be one x value. Let's consider a graph with a line that curves and intersects x=2 twice. This would mean that if you plug 2 into the function you would get two answers. However, this is not possible as plugging in any value to x will result in only one answer. For example, if y= 4x + 3, no matter how many times I plug a number in there, I'm always going to get the same y value, and this is true for all real functions.
Hi, seems like the answer is f(x) = x - 4
Edit: this was my original answer, but I was apparently completely out of my mind when I wrote it. The correct answer is f(x) = -4x + 50, as I stated below. I'm very sorry for any trouble I caused
Answer: 
Step-by-step explanation:
Perpendicular lines have slopes that are negative reciprocals, so as the slope of the given line is -5/4, the slope of the perpendicular line is 4/5.
Substituting into point-slope form,
65 x6 = 390
80 x 3= 240
390+240 = 630
Area of a square= l²
= 8×8 = 64 in²
Area of a circle= πr²
= π × 4²
= 50.3 in²
Difference = 64 - 50.3 = 13.7 in²
