某人买13个鸡蛋,5个鸭蛋,9个鹅蛋共用去12.7元.买3个鸡蛋2个鹅蛋一个鸭蛋共用2.8元,试问买鸡蛋鸭蛋鹅蛋

13X+5Y+9Z=12.7------⑴
3X+Y+2Z=2.8--------⑵
求X+Y+Z的值.
⑵×5得：15X+5Y+10Z=14------⑶
(3)-(1)得2X+Z=1.3.(4)
(1)×2得26X+10Y+18Z=25.4.(5)
(2)×9得27X+9Y+18Z=25.2.(6)
(5)-(6)得Y-X=0.2.(7)
(4)+(7)得2X+Z+Y-X=1.3+0.2
X+Y+Z=1.5