Question 1144730
first x
second y
third z
{{{system(x+y+z=30,x+y=2z,2x+3=y+z)}}}


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First two equations
{{{system(x+y=30-z,x+y=2z)}}}

{{{30-z=2z}}}

{{{30=3z}}}

{{{highlight_green(z=10)}}}
The third number found.





(Better to continue solve for x and y and check if solution for x,y,z work in the system, and in last equation of original description)