4X+2(50-X)= 140
4X+ 100-2X= 140
2X=40
X=20
50-20=30 (only) 20+30=50 (only)
A: There are 20 turtles, 30 cranes and 50.
Note: 2X is the total number of turtle eyes, and 100-2X is the total number of crane eyes. Because every crane has two eyes, (100-2X)÷2=50-X is the only number of cranes.