a)a-9/16a=5 целых 1/4 16\16а-9\16а=21\4 7\16а=21\4 а=21\4*16\7 а=12 b)(3,1d-d):0,2=1,05 2.1d=1.05*0.2 2.1d=0.21 d=0.21:2.1 d=0.1