Ok, James. The idea here is to isolate the variable n. That is, to move every term that is not n to the other side of the equation. We do that by adding, subtracting, multiplying or dividing. Let me demonstrate with one or two of your examples, and then you can carry on with the others.
$\displaystyle 2n=4xp-6$
This one is fairly easy since most of the terms without n are already on the right side of the equation. All we need to do is eliminate the 2 that is multiplied by n. We do this by perfoming the inverse operation of multiplication which is division. H
Hence, divide all terms by 2:
$\displaystyle \frac{2n}{2}=\frac{4xp}{2}-\frac{6}{2}$
Simplifying, we get:
$\displaystyle n=2xp-3$
For the next one,$\displaystyle 3m-n=4s$
You first must move or transpose the 3m from the left side to the right side.
Since 3m is positive on the left, we must add its opposite to remove it, but we must add its opposite to the right side as well to keep things balanced.
$\displaystyle 3m+(-3m)-n=4s+(-3m)$
$\displaystyle 0-n=4s-3m$
$\displaystyle -n=4s-3m$
Since n is negative on the left, we must multiply all terms by -1 in order to achieve the desired result. Thus,
$\displaystyle -(-n)=-(4s-3m)$
Finally.
$\displaystyle n=-4s+3m \ or \ n=3m-4s$
You might want to take a look at this site for some step by step instructions:
Solving Literal Equations