3. (20 pts) Figure shows a distillation column of Formosa Plastics Corporation. The feed contains 20 mol% 2-butene and 80 mol% isoprene, and top product is mainly 2-butene with a small amount of isoprene. The bottom of the column contains 70 mol% isoprene and 30 mol% 2-butene. Calculate the percent recovery of 2-butene in top product. Hint: percent recovery = the mass of top product composition/the mass of feed composition.