11. a+b+c=31,23
a=b-7,29=>b=a+7,29
a=c/5=>c=5a
a+a+7,29+5a=31,23
7a+7,29=31,23
7a=31,23-7,29
7a=23,94=>a=23,94:7=>a=3,42
b=a+7,29=>b=3,42+7,29=>b=10.71
c=5a=>c=5 ori 3,42=>c=17,1
12. (6km+10km)/(1h+1h)=16hm/2h=8km/h
nu sunt sigura..asa am gasit formula aici
