3 frati 786 lei
I /-----/-----/
II /-----/+13
III /-----/-----/-----/-----/+13x4
TOTAL 786
7segmente+13x5=786
7segmente+65=786
7segmente=786-65=721
1segment=103
I frate 2 x 103 = 206 lei
II frate 103+ 13 = 116 lei
III frate 103x4+13x4=412+52 = 464 lei
proba: 206+116+464=786