1*2*3+3*6*9+7*14*21/1*3*5+3*9*15+7*21*35
=1*2*3+3*1*3*2*3*3+7*1*7*2*7*3/1*3*5+3*1*3*3*3*5+7*1*7*3*7*5
=1*2*3+3³*1*2*3+7³*1*2*3/1*3*5+3³*1*3*5+7³*1*3*5
=1*2*3(1+3³+7³)/1*3*5(1+3³+7³)
=1*2*3/1*3*5
=2/5