Derek bought 6.00 worth of 21 cent stamps and 41 cent stamps.

we have the expression
[tex]0.21s+0.41(s-2)=6.00[/tex]Solve for s
that means ----> isolate the variable s
[tex]0.21s+0.41s-0.82=6.00[/tex]Combine like terms
[tex]\begin{gathered} 0.62s=6.00+0.82 \\ 0.62s=6.82 \end{gathered}[/tex]Divide by 0.62 both sides
[tex]\begin{gathered} s=\frac{6.82}{0.62} \\ s=11 \end{gathered}[/tex]