a+b+c=61
c=2a+18
c=b+25
2a=c-18
a=(c-18):2
b=c-25
(c-18):2+c-25+c=61
(c-18):2+2c=61+25
(c-18):2+2c=86 (x cu 2)
c-18+4c=172
5c=172+18
5c=190
c=190:5
c=38 t rosii s-au livrat in a treia zi
b=38-25
b=13 t rosii s-au livrat in a doua zi
a=(38-18):2
a=20:2
a=10 t rosii s-au livrat in prima zi