As shown in the diagram above. a lever resting on a fulcrum has weights of ~$w_1$~ pounds and ~$w_2$~ pounds, located ~$d_1$~ feet and ~$d_2$~ feet from the fulcrum. The lever is balanced and ~$w_1d_1=w_2d_2$~ . Suppose ~$w_1$~ is 50 pounds and ~$w_2$~ is 30 pounds. If ~$d_1$~ is 4 feet less than ~$d_2$~ ,what is ~$d_2$~, in feet?