`Answer:`
a. \(5x-[2x+1-\left(2x-3\right)-\left(4x+1\right)]\)
\(=5x-\left(2x+1-2x+3-4x-1\right)\)
\(=5x-2x-1+2x-3+4x+1\)
\(=\left(5x-2x+2x+4x\right)+\left(-3-1+1\right)\)
\(=9x-3\)
b. \(\left(-3x^2+2x-1\right)+\left(4x^2-2x+3\right)\)
\(=-3x^2+2x-1+4x^2-2x+3\)
\(=\left(-3x^2+4x^2\right)+\left(2x-2x\right)+\left(-1+3\right)\)
\(=x^2+2\)