No problem! Let's begin
2x + 3y + 7x - 2y... the answer IS that simple.
although the 1 can be omitted before y because if there is no coefficient 1 is assumed.
a* + 3a + 4 + a* + 7a - 5... you do the same thing as before, put the like terms together, except a* is different to a, despite them both having a. So a* + a* gives 2a*, 3a + 7a gives 10a and 4-5 = -1, so the final answer is 2a* + 10a -1
x(x + 4)... you simply have to multiply term in the brackets by x, so it becomes (x times x + 4 times x), or x* + 4x
2(3x+2) ... same principle, except now you have to do it to both brackets. So 2(3x+2) = (2 times 3x + 2 times 2) = 6x+4, and -2 (x+4) (note that the negative must be included) = (-2 times x + -2 times 4) = -2x -8. Now add all of them together and you get 6x+4-2x-8 = 4x-4
(x+3) (x-4)... now this gets a bit trickier. you have multiply each of the terms in the first bracket with each of the terms in the second bracket. I would draw a table like this
times x -4
x x* -4x
3 3x -12
So you multiply each term in the left column with each term in the top row, then you add them together. x*+3x-4x-12 = x*-x-12.
(x-3) (x-9)... same principle.
times x -9
x x* -4x
-3 -3x +27 (negative times negative = positive)
so x*-4x-3x+27 = x*-7x+27(x+10)*... this is the same as (x+10)(x+10), then all you have to do is do the same thing as the previous two quesitons. See if you can do this yourself.
If you need help, ask again.