The static friction formula is
[tex]\begin{gathered} F_s=\mu_sN \\ \mu_s=\frac{F_s}{mg} \end{gathered}[/tex]As you can observe, the normal force is equal to the weight force.
[tex]\mu_s=\frac{20N}{80N}=0.25[/tex]Therefore, the value of the coefficient of static friction is 0.25.
