Easy: Graphs of Straight Line 
I can't exactly figure out how to work this out.
Well I know the equation for a straight line is $y = mx + c$
$c = gradient$
Therefore if I multiply $3$ by the number $x$ to get the gradient $6$ and $2$ I can work out which is line is which...
With $y = 3(x + 2)$ I tried to expand but then I got confused.
Can someone explain in easy terms? Thanks guys.

Syntactical side note: $m$ is called the gradient, $c$ is called the $y$-intercept.
To find the correct equation for $A$, just look at the $y$-intercept of $A$: it's $6$.
This means that $A$ must be of the form $y = mx + 6$, wich only one of your equations satisfies. Note that
$$a\cdot(b+c) = a\cdot b + a\cdot c$$
for any real numbers (also variables) $a,b$ and $c$.
