d = 2d/5 + 2d/5 x 2/3 + 40
d = 2d/5 + 4d/15 + 40
15d = 6d + 4d + 600
15d - 6d - 4d = 600
5d = 600
d = 120 km
2d/5 = 2*120/5 = 240/5 = 48 km (prima zi)
2/3*48 = 96/3 = 32 km (a doua zi)
40 km (a treia zi)
