\(a,\left(7,8+2,2\right)\times1,2\\ ◻C1:\\ =10\times1,2\\ =12\\ ◻C2:=7,8\times1,2+2,2\times1,2\\ =9,36+2,64\\ =12\\ b,\left(6,75+3,25\right)\times4,2\\ ◻C1:=10\times4,2=42\\ ◻C2:=6,75\times4,2+3,25\times4,2\\ =28,35+13,65\\ =42\\ c,\left(9,6-4,2\right)\times3,6\\ ◻C1:=5,4\times3,6\\ =19,44\\ ◻C2:=9,6\times3,6-4,2\times3,6\\ =34,56-15,12\\ =19,44\)