Solving a System of Equations
Below is a command that should be useful for your homework. Make sure to follow the syntax exactly, including the "double equals sign" == when writing an equation, write the equations within by curly brackets, and that ask to solve for all relevant variables, here they are a, b, and c. Remember, you must press shift-enter to evaluate this cell:
In[]:=
Solve[{2a+3b+2c1,3a+5b+1c5,6a+12b+6c7},{a,b,c}]