7.69-5.22+15.97=(7-5+15)+(0.69-0.22+0.97)=17+(0.6-0.2+0.9)+(0.09-0.02+0.07)=17+1.3+0.14=18.44
7.69-5.22+15.97=7.7+16-(5.22+0.04)=18.44