Answer:
l = (P -2w)/2
Step-by-step explanation:
When you're working any "solve for ..." problem, first you look to see where the variable of interest is and what is done to it.
If it is only found on one side of the equation, as here, then you're in luck. If it is only found in one term, as here, you have even better luck.
Identify all the terms on the side of the equation where the variable is located that do not contain the variable. Add their opposite to both sides of the equation. The result will be a term containing the variable, equated to a bunch of other stuff.
... P -2w = 2l . . . . . we added -2w to both sides of the equation
Now, we divide the equation by the coefficient of the variable.
... (P -2w)/2 = (2l)/2
... (P -2w)/2 = l . . . . . . simplify. This is the solution you're looking for
If you like, you can distribute the multiplication by (1/2) to get
... l = P/2 - w
