ANSWER:
D) z = 1/5 or z = 4
STEP-BY-STEP EXPLANATION:
We have the following equation:
[tex]5z^2-21z+4=0[/tex]We solve by factoring like this:
[tex]\begin{gathered} 5z^2-21z+4=0 \\ -21z=-z-20z \\ 5z^2-z-20z+4=0 \\ z(5z-1)-4(5z-1)=0 \\ (5z-1)(z-4)=0 \\ 5z-1=0\rightarrow z=\frac{1}{5} \\ z-4=0\rightarrow z=4 \end{gathered}[/tex]Therefore, the solution of the equation is z = 1/5 or z = 4
