In your spreadsheet from Video 3, make sure that you have solved the original small example problem (change the spinal cord limit back to 5 and re-solve if you have changed it, and make sure the objective value is 22.75).
Now, change the weight for the spinal cord term in the objective to 5.
Without re-solving, what does the objective value of the current solution change to?
The term SUMPRODUCT(B14:B19;F5:F10) in the objective (corresponding to Voxel 5) should now be 5*SUMPRODUCT(B14:B19;F5:F10). This changes the objective value to 42.75.
Now re-solve the model. What does the objective change to?
You can resolve the model by going to Solver, and just hitting Solve. The new optimal objective function value is 25.666667.
Notice how we are now giving a smaller dose to the spinal cord!