Well, it would be good if you could provide more information. You can
use solver for finding optimum solutions. MMULT can solve linear
equations as an array.
Can be done very easily with Solver or matrix functions.
Which are you more comfortable with?
Send example of a system of equations you want solved.
best wishes
PS My book A Guide to MS Excel for Scientists and Engineers is available in
Polish as Microsoft Excel w nauce i tecnics ISBN83-7243-240-6. It shows both
methods