a= suprafata arata de primul tractor pe ora
b= suprafata arata de al 2-a tractor/ora
15×(a+b)=1/6, unde 1 este lucrarea
90a+90b =1
12a+20b=20%*1
60a+100b=1
a=(1-90b)/90
60*(1-90b)/90+100b=1
2*(1-90b)/3+100b=1
2-180b+300b=3
120b=1
b=1/120
1:1/120=120 ore tractorul 2
a=1-90*1/120)/90=(1-3/4)/90=1/360
1:1/360=360ore tractor 1
2.
a=suma elev 1
b=4a/5=suma elev 2
c=suma elev 3
6 1/2=13/2
9 1/8=73/8
b=13k/2=4a/5 k=8a/65
c=73k/8=(73*8a/65)/8=73a/65
a+4a/5+73a/65=1520
65a+52a+73a=98800
190a=98800
a=520 lei
b=4*520/5=416 lei
c=73*520/65=584 lei