 " The Old Man and the Lisa " is the twenty @-@ first episode of The Simpsons ' eighth season . It first aired on the Fox network in the United States on April 20 , 1997 . In the episode , Mr. Burns becomes bankrupt and asks Lisa to help him become rich again . She helps him on the condition that he will lose his evil manners , and the two start making money recycling cans . After a while Mr. Burns has made enough money to start his own recycling plant . However , his true colors are revealed when Mr. Burns shows that , inside the plant , he makes a multi @-@ purpose edible compound made of squished sea life . He then sells the plant for US $ 120 million and offers Lisa 10 % of his profits , but she declines . 
