2X+ 170=4×(80-X)

2X+ 170=320-4X

2X+4X=320- 170

6X= 150

X=25 (only)

80-25 = 55 (only)

A: There are 25 chickens and 55 rabbits.

2、

Suppose: there are x rabbits and X+3 chickens.

4X+2×(X+3)=42

4X+2X+6=42

6X=36

X=6 (only)

6+3=9 (only)

A: There are 9 chickens and 6 rabbits.