So the length is 4*28=112mm
The width would be calculated like this:
you draw an equilateral triangle in the middle with sides or 2r(56mm). The based on pythagorean theorem u know that
h=rad(56^2-28^2)=48.497
28+28+h=104.497
The area would be S=l*w which is 11703.7113mm
The y intercept is when x is 0. So, we have to plug in 0 for x. You can do this in many different ways as well.
7(0)-4y=8
-4y=8
Divide both sides by -4.
Y=-2
So, the Y intercept is -2 (0,-2).
The expression 30 + 12 can be rewritten as 2x(13+8)