IM using my brothers account and so Im kinda stuck on these questions thanks
Hi there,
Just work through it step by step, each time subbing what you know
So we know that
$\displaystyle L=\frac{1}{3}(E-24x)$
we're told what E is so we can now write.
$\displaystyle L=\frac{1}{3}(98-24x) = \frac{98}{3}-8x$
Now we can put this value of L into our formula for A, which gives us
$\displaystyle 448 = 12x^2 +12\big(\frac{98}{3} - 8x \big)x$
$\displaystyle 448 = 12x^2 + 392x - 96x^2$
Rearrange a bit
$\displaystyle 84x^2 - 392x + 448= 0$
All the terms have a common factor of 28, so we can divide through to get
$\displaystyle 3x^2 - 14x + 16 = 0$
as required