If you are getting the incorrect answer then probably the worksheet is set up incorrectly or the Solver parameters are incorrect. Don't forget to set the solver options to assume a linear model and that the variable values are non-negative.
Here is how I set up my worksheet:
The values in the "Constraints" column are entered as numbers. The values in the "Results" column are calculated values. I used matrix multiplication to find all of the results at the same time but you could also enter each result as a separate Excel expression.
Here are the Solver parameters for my worksheet:
Notice that we are setting the target to its minimum value rather than its maximum as we have done before.