Answer :
[tex]S_A=\frac{1}{2}LP+B\\\\\frac{1}{2}LP+B=S_A\ \ \ \ \ \ |subrtact\ "B"\ from\ both\ sides\\\\\frac{1}{2}LP=S_A-B\ \ \ \ \ |multiply\ both\ sides\ by\ 2\\\\LP=2S_A-2B\ \ \ \ \ \ |divide\ both\ sides\ by\ "L"\\\\P=\frac{2S_A-2B}{L}[/tex]
