Question

http://prntscr.com/4vlqj3

Answer 1

\[S = B+\frac{ 1 }{ 2 }Pl\] First start by subtracting B. \[S - B = \frac{ 1 }{2 }PL\] Then multiply by 2/1 (the inverse) \[S - B \times \frac{ 2 }{ 1 } = \frac{ 1 }{ 2 } \times \frac{2}{1} \times Pl\] On the right side, 1/2 and 2/1 will simply cancel each other. And 2/1 is an improper fraction. It can simply be expressed as 2. \[S - B + 2 = Pl\] You're final step is simply dividing be l.

Answer 2

I'm sorry. S -B + 2 would be expressed as 2(S - B)

So you have 2(S - B) = Pl; you just need to divide by l.