[tex]\begin{gathered} 2300=275\times L+400\times S \\ \text{if the person spent in Los angeles 4 day,} \\ \text{it will cost}\Rightarrow275\times4=1100\text{ \$} \\ \text{if the person spent in San Francisco 3 day,} \\ it\text{ will cost}\Rightarrow400\times3=1200\text{ \$} \\ So\text{ the total spent is,} \\ \Rightarrow1100+1200=2300\text{ \$} \end{gathered}[/tex]