@tutors,
VBscript as well as other tools he mentioned are programming languages. If you don't know anything about programming, it's probably not going to be the fastest method for you, as you'd have to learn programming first, which is a good semester's worth of work in college (ok, on basic level maybe a little less than that). So I suggest you to stick with Excel. Again, it takes a little bit of knowledge in that area, but in my experience, there are many more those who know Excel than those who know a programming language.
The way I set it up for first problem, was numbers from 1 to max number of 16" pizzas to fill the necessary area in one column, then a forumla to calculate the needed number of 12" pizzas with given number of 16" pizzas, then next column total cost of buying the two in set numbers... Then looked for minimal total cost, and viola... For todays problem I added a constant number of 22" pizzas and started with whatever the area I needed after buying that many, and of course added the cost to total, and then manually by hand flipped through different numbers of 22" ones to see what will give me the best answer... I am afraid that giving away actual formulas to calculate these numbers would pretty much equal to giving away the answer, so I'll keep it at that...
LEM.