Solution: Let the price of each pencil be X yuan.
6X+ 1.5×6= 13.8
X=0.8
2, lack of known conditions, unable to answer.
3. Equivalence: the price of the table+the price of the chair = the total amount of money.
Solution: The price of a chair is X yuan, then the price of a table is 3X yuan.
X+3X= 120
X=30
So the price of the table is: 30×3=90 yuan.
4. Equivalence relationship: rabbit feet-chicken feet = 28 rabbits with more feet than chicken feet.
Solution: There are X chickens and X rabbits in the cage.
4X-2X=28
X= 14