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.
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
