a) `P + (3x^2 - 4 + 5x) = x^2 - 4x`
`=> P= x^2 - 4x - 3x^2 + 4- 5x`
`=>P = (x^2 - 3x^2) - (4x + 5x) +4`
`=> P= -2x^2 - 9x +4`
b) `Q - 14y^4 + 6y^5 - 3= -12y^5 + y^4 -1`
`Q= -12y^5 + y^4 - 1 + 14y^4 - 6y^5 +3`
`Q= (-12y^5 - 6y^5) + ( y^4 + 14y^4) - (1-3)`
`Q= -18y^5 + 15y^4 +2`