So the formula say 4 pounds of fertilizer for 160 square feet and he has to made for 200 square feet so we can made a rule of 3 so:
[tex]\begin{gathered} 4\to160 \\ x\to200 \end{gathered}[/tex]and the equation will be:
[tex]\begin{gathered} x=\frac{200\cdot4}{160} \\ x=5 \end{gathered}[/tex]So he need 5 pounds of fertilizer