You have a choice to build a small new plant, do nothing (the value of this is zero), or build a large plant. We'll use Net Present Value to compute this. Here's the formula:
The likelihood of high revenue plus the likelihood of low revenue minus fixed costs (the price of the factory).
Small plant:
70 percent chance of high revenue of 10 million
30 percent chance of low revenue of 5 million
Plant costs to make the factory - 3 million
Large Facility
80 percent chance of high revenue of 15 million
20 percent chance of low revenue of 7 million
Plant costs to make the factory - 8 million