Matrix Problem with to manny variables :s

[Totter]

The relationship between the quantity (in thousands of tons) of three types of ore which is mined on a certain day at a mine, is given by the following system of equations:
r + s + t =12
2r -s +3t = 18
6r - 3s +t= 6
Determine the quantity of each type of ore which is mined using the INVERSE of the coefficient matrix.

Now I tried with Cramers rule but didnt really amount to much.I know how to get the Inverse but how do I work it out if I have it?

Thanks

 

[rcgldr]

Convert the set of equations into a matrix format, M x vertical column of {r, s, t} = vertical column of {12, 18, 6}, then {r, s, t} = M^-1 x {12, 18, 6}, where M¹ is the inverse matrix.