(30^-1+60^-1+80^-1)^-1
(30−1+60−1+80−1)−1=(130+160+180)−1=(60⋅80+30⋅80+30⋅6030⋅60⋅80)−1=30⋅60⋅8060⋅80+30⋅80+30⋅60=1440009000=16