The whey is a 4.7kg bag(= ~10lbs), so thats 4700 grams, the serving size is 30 grams so your looking at about 155 servings which would last you a good bit. Take it once a day like.
The
serious mass its says has 16 servings but if you half the serving size you'd get 32 then obviously. You be better of taking half a serving i think because your body can only take in so much nutrients at any one time & basically you'll shit out the rest!
If you aim to get most of your nutrients from 4-6 solid meals a day & then throw on top 1 protein shake and 1 half serious mass shake you'd be flying. Or even 3 solid meals, descent breakfast, lunch & dinner and then one of each shake. You get the idea anyway.