Question 196141
Let the unknown masses be {{{a}}}, {{{b}}}, and {{{c}}}
{{{a + b = c + 9}}}
{{{b + c = a + 15}}}
{{{c + a = b + 27}}}
From those I get:
{{{a + b - c = 9}}}
{{{-a + b + c = 15}}}
{{{a - b + c = 27}}}
Adding the 1st two:
{{{2b = 24}}}
{{{b = 12}}}
Adding the 2nd two:
{{{2c = 42}}}
{{{c = 21}}}
And from the 1st:
{{{a + b - c = 9}}}
{{{a + 12 - 21 = 9}}}
{{{a + 12 = 30}}}
{{{a = 18}}}
The unknown masses are 18g, 12g, and 21g