add.\n$(8s^{4}+9s^{3}+2s^{2}+5s + 6)+(-s^{4}+9s^{3}-6s^{2}+8s - 7)$

Explanation:

Step1: Combine like - terms of $s^4$

$(8s^{4}+(-s^{4}))=(8 - 1)s^{4}=7s^{4}$

Step2: Combine like - terms of $s^3$

$(9s^{3}+9s^{3})=(9 + 9)s^{3}=18s^{3}$

Step3: Combine like - terms of $s^2$

$(2s^{2}+(-6s^{2}))=(2-6)s^{2}=-4s^{2}$

Step4: Combine like - terms of $s$

$(5s + 8s)=(5 + 8)s=13s$

Step5: Combine constant terms

$(6+(-7))=6 - 7=-1$

Answer:

$7s^{4}+18s^{3}-4s^{2}+13s - 1$