7 grinzi brad...12 grinzi stejar...750 kg /×3
3 grinzi brad...8 grinzi stejar....450 kg /×7
21 grinzi brad...56 grinzi stejar....3150 kg
21 grinzi brad...36 grinzi stejar...2250 kg
scadem cele doua relatii
20 grinzi stejar ....900
1 grinda stejar =900:20=45 kg
8 grinzi stejar =45×8=360
1 grinda brad =(450-360):3=90:3=30 kg