You want to combine like terms :). This means the terms that are the same will be added or subtracted depending on their sign at the beginning.
1) x^2 +x+3-4x
Rearrange first to put like terms together
X^2 +x-4x +3
Your answer to a would be…
x^2 -3x+3
Lmk if you would like me to do another problem for extra practice!
Hope that helps!