Question

How do you solve for L?

L=5B
L+7=3(B+7)

Answer 1

You first plug in 5B for L in the 2nd equation and you get 5B+7=3B+21 (distributive property). Then you simplify and you get B = 7. Then you plug 7 back in the first equation and get L = 35.

Answer 2

remember
a(b+c)=ab+ac
and you can do ANYTTHING to be
L=5B
divide both sides by 5
L/5=B
sub L/5 for B in other equation
L+7=3((L/5)+7)
distribute
L+7=(3L)/5+21
minus 7 both sides
L=(3L)/5+14
time boths sides by 5
5L=3L+70
minus 3L both sides
2L=70
divide 2
L=35