The rate at which natural gas was consumed (in billions of cubic feet per year) by the industrial sector for lease and plant fuel can be approximated by () = 32 − 14 1131, 0 ≤ ≤ 25, where = 0 corresponds to the start of the year 2000. Find the value of ∫ () 25 20 , and explain what that value means in practical (“real life”) terms.