Maths help desperately needed

okay, so these concepts are really basic to get.

firstly, 3x=9 solve for x.
think of 9 apples. now divide the 9 apples into 3 groups. how many apples do you have in each group? it would be 3, correct?
the principle of algebraic questions is basically working backwards to find the x. in other words, your question is asking "3 times SOMETHING equals to 9" (since this is a simple equation you would easily know that the answer would be 3)

the way i learnt to figure these out is the concept of opposite signs.
+ is the opposite to - (vice versa) and
multiply is the opposite of divide

so once you know this, its pretty easy from there:
eg. 2+x=5
to find x, you do the OPPOSITE sign to it (therefore you go 5-2)
therefore x=3 (check your answer, does 2+3=5, yes so you are correct)
now for "harder" ones.
3x=9
to find x, you do the OPPOSITE sign which is divide (therefore you go 9/3)
therefore x=3 (and check)

with the a=pi x r squared just sub in the 3, and solve it like a normal equation

btw. it seems that you are in senior year. if you dont understand these concepts, i dont think you should be thinking of studying math in uni. this is basic grade 6 stuff... :P

good luck on your exam!!

If you don't understand algebra, start with arithmetic and work your way upwards.
For example, if the equation was 3x = 9, ask yourself, what is x?
x is an unknown number, and can be any number whatsoever.
Try substituting a few numbers in for x.
Eg. If you let x = 1 then 3*1 = 3 and the equation doesn't make sense.
If you let x = 2, then 3*2 = 6 and the equation doesn't make sense.
If you let x = 3, then 3*3 = 9 and the equation makes perfect sense.
Therefore, x = 3.
Whatever you do to one side of the equation, you do to the other side.
For example: If 3 + 4 = 7, I can decide to take away 4 from both sides of the equation