Question 226522
1) (9x^8 - 8x^3 + 2x^2 + 4) + (3x^7 + 5x^3 - 9x) 
Add like terms.  "Like terms" have the same exponent.
= 9x^8 + 3x^7 - 3x^3 + 2x^2 - 9x + 4
It's a good idea to write it (or print it) and cross them off as you go, so as not to miss any.
That's all there is to it, tho.  x^3 was the only term in both polynomials in this one.
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2) Simplify the expression, and identify the constants, coefficients, and 
variables in the simplified expression. 3/a * b/8
= 3b/8a
a and b are variables (I assume, it's not specified otherwise). 3 and 8 are coefficients.
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You can find a lot of info on things like this on google.