Question 315235
You can get a value of each variable in terms of the constants and other variables.
As an example,
{{{3a-5b+5c=21}}}
{{{3a=21+5b-5c}}}
{{{a=(21+5b-5c)/3}}}
From what you write, I'm assuming that's not what you're looking for.
To get a numerical value for 3 variables, you need 3 independent equations that describe the relationships between the three variables.