have i done this correctly? was unsure about the 18/2 part?
Given an equation of the form
$\displaystyle ax^2 + bx +c=0,$
we can find solutions for $\displaystyle x$ using the formula
$\displaystyle x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}.$
Check that you have used this formula correctly. An easy way to tell if you have the right answer is to substitute your values for $\displaystyle x$ back into the original equation to see if you get the right answer i.e try and work out whether $\displaystyle (4.45)^2+2(4.45)-3.5$ really equals zero. If not then you need to check your calculations carefully.
there are two problems with your solution:
1) EVERYTHING goes over the 2, not just "the square root part"
2)you should wind up with:
$\displaystyle \frac{-2 \pm \sqrt{18}}{2}$
it's ok to leave it like this, but if you want to simplify:
$\displaystyle \sqrt{18} = \sqrt{2}\sqrt{9} = 3\sqrt{2}$.
neither:
$\displaystyle \frac{-2 + 3\sqrt{2}}{2}$ nor $\displaystyle \frac{-2 - 3\sqrt{2}}{2}$ are even close to either one of your "proposed" answers 2.12 or 2.45. there is no √6 involved in the correct solution.