Full Rate: That is the rate per acre if you wanted a pure stand of that one variety.
lbs per acre: That is what you select for your blend. For example, 13lbs of cowpeas would be 19% of the full rate of 68lbs for pure stand.
% full rate: This is the overall total that your blend is adding up to. This is where the total percentage guidance of 120%-150 comes in. As long as the sum of your percentage rates is around 100%, or more if you've got sketchy seeding methods or questionable moisture, you'll have a complete blend that should cover your ground.
From there, you have to chop your calculations up or down depending on the size of your plot. If you have a two acre plot, multiply your seed pounds by 2. If it's a half acre, you divide by 2.
Hope that helps. Hope my leg gets better so I can go to work tomorrow. There isn't enough content flowing on HT today to keep me occupied.