a=lungimea santului sapat
5a/18=lungimea sapata in 1 zi
a-5a/18=(18a-5a)/18=13a/18 =rest dupa 1 zi
(13a/18) x 2/5 = 26a/90 lungimea sapata in a 2-azi
5a/18+14=lungimea sapata in a 3-a zi
5a/18+26a/90+5a/18+14=a
25a+26a+25a+14x90=90a
14a=14x90
a=90 m
1 zi 90x5/18=25 m
a 2-a zi 90-25=65 65 x2/5=26 m
a 3-a zi 25+14=39 m