Write an equation you can use to find the length of the rectangle

We just need to know the perimeter
so say we only know the width 
which is 10
and the perimeter which is 30
hint( perimeter is all of the sides added up
anyways so we know that theres 2 sides that are ten so that gives us 
30 - 20 = 10
but there are 2 more sides to lets divide by 2 
10 ÷ 2 = 5 
so the length would be 5 
heres the equation
P = perimeter 
W = width
L = length
s
P - 2w = L ÷ 2

:P hope this helps