6.45*2.3+7.7=6.45*2.3+10-2.3=2.3*(6.45-1)+10=2.3*5.45+10=12.535+10=22.535
6.45*2.3+7.7=6.45*(2+0.3)+7.7=6.45*2+6.45*0.3+7.7=12.9+1.935+7.7=22.535