Answer:
18 units
Step-by-step explanation:
So let's list out the sides.
for the first square let's just call them x
for the second square then they would be x+5 and x-3
So let's write out their areas we will cal the area of the first one z
x*x = z
(x+5)*(x-3) = z+21
since z = x^2 we can set up the second equation as a quadratic.
(x+5)*(x-3) = x^2 + 21
x^2 - 3x + 5x - 15 = x^2 + 21
But look, the x^2s cancel out
2x - 15 = 21
2x = 36
x = 18
Test it out and see if it fits the description, And if you don't understand anything just let me know so I can explain more.
Answer:

From this, you can tell it's in slope-intercept form, has a slope of -1/2, and a y-intercept of -4.
I've included a picture of what this equation looks like.
Answer:
13
Step-by-step explanation:
-2x + 6 = -20
Step 1 subtract 6 from both sides
6 - 6 cancels out
-20 - 6 = -26
We now have -2x = -26
Step 2 divide both sides by -2
-2x/-2 = x
-26/-2 = 13
We're left with x = 13