Answer:
They want you to have a good "grasp" of algebra... since you're asking about this I'm going to guess you don't feel that comfortable with it ... so I'll go in detail below. Even thought this is exactly what your math teacher is supposed to be teaching you.. ask your math teacher if I can have part of their salary :) $$
Explanation:
in Question 18 , they are asking to solve for y . what that means is they want an equation that looks like y= (some stuff) In math terms they are asking you to isolate the y ... which is the part your math teacher should have told you.. were you just not listening? :P Anyway, soooo to solve for y we want to get y by it self.. on one side of the = sign and everything else on the other.. to do this use the order of operations ... but.. for doing algebra it has to be done in reverse order :0.... which i'm sure your math teacher hasn't mentioned and partly why algebra is so difficult.
soooo solve for 'y' ( isolate y )
12x-4y=20
-4y=20-12x
y=(20-12x)/-4
Yes, I know.. that answer is not very "satisfying" but. that is solved for "y"
for Question 20 it's just straight algebra, no numbers.. it's more abstract...and solve for R ( isolate 'R') to get R by itself
P=(R-C) / N
I'm multiplying by N first b/c the next thing in those parenthesis and when you do the order of operations you'd usually to that first but remember we are going back wards in operations.. sooo multiply both sides by N
P*N=R-C ..
now that R-C is no longer in parenthesis we can do that addition of C to both sides.. this is kinda tricky b/c of how the R-C were both over the N anyway...
P*N +C=R
another way to think of this one.... maybe you don't want to and you can just skip this part if you want to be done...
P=(R-C)/N
P=R/N - C/N now we can do addition first .. like I was mentioning above
P+C/N = R/N multiply both sides by N
N(P+C/N)=R b/c N/N =1 just drop it from the R'
P*N +C =R we end up at the same place but my a different route.