$a)$

$u\left(x\right)+w\left(x\right)=17x^4-\underline{14x^2}+\underline{\underline{7x}}-\underline{\underline{\underline{5}}}+6x^3+\underline{11x^2}-\underline{\underline{5x}}+\underline{\underline{\underline{5}}}=17x^4+6x^3-3x^2+2x$

$st\left(u\right)=4$

$st\left(w\right)=3$

$st\left(u+w\right)=4$