To solve the system of equation use substitution method:
1. Solve s in the first equation:
[tex]s=500-n[/tex]2. Substitute in the second equation the s for the value you get in step 1:
[tex]5(500-n)+10n=4000[/tex]3. Solve n:
[tex]\begin{gathered} 2500-5n+10n=4000 \\ -5n+10n=4000-2500 \\ 5n=1500 \\ n=\frac{1500}{5} \\ \\ n=300 \end{gathered}[/tex]4. Use the value of n to solve s:
[tex]\begin{gathered} s=500-n \\ s=500-300 \\ s=200 \end{gathered}[/tex]