Is there more information for this question? It seems like you forgot something.
Standard from is ax² + bx + c = 0
Just do the opposite of -12 on both sides
ANSWER: x² - 4x + 12 = 0
That would be 29.7
I hope this helps
Dy/dx=25, 35, 45, 55
d2y/dx2=10,10,10 (this constant just proves that it is a quadratic relation)
Now we can set up a system of equations for ax^2+bx+c
16a+4b+c=80, 9a+3b+c=45, 4a+2b+c=20 getting differences
7a+b=35, 5a+b=25 and again
2a=10, a=5, making 7a+b=35 become:
7(5)+b-35, b=0, making 4a+2b+c=20 become:
4(5)+2(0)+c=20, c=0 so
y=5x^2
So the constant of variation for this quadratic is 5.
7.5cm
lets take point K represent lenght from M to perimeter of circle.
r is radius
KM= r-OM= r-4.5cm
now lets draw line from O to A (OA)
we get triangle.
hypotenuse is OA and it equals r(radius)
ab=12 cm. so another side of the triangle (AM) is 12/2=6cm. and the last side of the triangle is 4.5(OM)
use pythaghorean theorem
squares of sides added = square of hypotenuse
20.25+36=r^2(our hypotenuse is radius)
56.25=r^2
r=√56.25=7.5cm