bearing in mind that the centroid in a triangle cuts each of the three medians in a 2:1 ratio.
since we know that A C = 12, let's split it in a 2:1 ratio then, cleary from the picture the larger is F C, so F C : A F is on a 2:1 ratio.

A, D and E are correct
given ( x - 4 ) is a factor then x = 4 is a root
the remainder on division by (x - 4 ) = 0 as indicated by the 0 on the right side of the quotient
(x - 4 ) is a factor of 3x² - 13x + 4 → A
the number 4is a root of f(x) = 3x² - 13x + 4 → D ( explained above )
thus 3x² - 13x + 4 ÷ (x - 4 ) = 3x - 1 → E
the quotient line 3 - 1 0
3 and - 1 are the coefficients of the linear quotient and 0 is the remainder
So you have a right angle triangle. You need to use trig for this, as you have two values you can figure out a third.
You know that you have
90 deg. angle
19 deg. angle
Therefor you have 71 deg. angle
sin19 = x/15
15sin19 = x
x = 2.2
Now do Pythagoras c^2-b^2=a^2
a = 14.8
So the sides are 2.2 and 14.8 units long. (If these numbers are wrong tell me and I'll edit answer)
The equation is Oy = 3/6x