21/{(2/3+2/5)*30/[(3+5/42)-(2+5/14)]}
=21/{(30*2/3+30*2/5)/[(3-2)+(5/42-5/14)]}
=21/[(20+12)/(1-5/21)]
=21/[32/(16/21)]
=(21*16/21)/32
=16/32
=1/2