p=2(l+b)
multiply the bracket by 2
(2)(l)=2l
(2)(b)=2b
p=2l+2b
move 2b to the other side
sign changes from +2b to -2b
p-2b=2l+2b-2b
p-2b=2l divide both sides by 2
p/2-2b/2=2l/2
cross out 2 and 2 for -2b/2= 1*-1*b=-b
cross out 2l and 2= 1*1*l=l
p/2-b=l
answer:
1=p/2-b