1/4 cup approx. 17.5 g
1/2 cup approx. 35 g
3/4 cup approx. 52.5 g
1 cup approx. 70 g
You can get real complex with math if you want and look at actual protein. Say you take a 1/2 cup of whey isolate and if it's 90% you'll have approx. 31.5 g of protein, but if you take a 1/2 cup of whey concentrate and if it's 80% you'll have approx. 28 g of protein. Then again, you'll never get the same amount in a scoop so I say to heck with the math.
I've ordered from them 3 times and haven't seen that little bonus bag. However, I just placed my 4th order and will check out my delivery next week.