Solving an equation means finding a value of a variable that make the equation true. This value is called the solution of the equation. A mathematical equation is just like a balanced equation. Both sides of the equation should be equal at all times. Whatever we do to one side, has to be done on the opposite side.
\(A=2(l+w)\)
\(\dfrac{a}{2}=l+w\) \(Divide \ both \ sides \ by \ 2\)
\(\dfrac{a}{2}-l=w\) \(Subtract \ l \ from \ both \ sides\)
\(w= \dfrac{a}{2}-l\)