(18-2,64) :1 3/5 = 9 3/5
18 - 2,64 =15,36
15,36 : 1 3/5= 15 36/100 : 1 3/5 = 15*100+36/100 :1*5+3/5= 1536/100:8/5=
1536/100*5/8=1536*5/100*8=7680/800=48/5=9 3/5
(4 3/7 + 1 2/3) * 2,1 =12 4/5
( 4+1) +(3/7+ 2/3) = 5+ 3*3 + 2*7 / 21 = 5+ 1 2/21= 6 2/21
6 2/21* 2,1 = 128/21 * 21/10=128 · 21/21 · 10 = 2688/210 = 64/5 = 12 4/5