<s>[INST] If $x+y+xy=3$ , $y+z+yz=8$ and $z+x+xz=15$ then Find $6xyz$. If $x+y+xy=3$ , $y+z+yz=8$ and $z+x+xz=15$ then
Find $6xyz$.  
How can I approach this problem?
I need some hints. Thanks. 
 [/INST] For convenience, we just need to look at one equation, $$x+y+xy=3  \implies (x+1)(y+1)=4$$
hence we define

 $a=x+1,b=y+1,c=z+1$

and we obtain 

 $ab=4,bc=9,ac=16$

You solve easily by that hint then.
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