I dont have a lot of time. Im going to help you with the first one, but please understand this is very hard to explain via internet.
1) For this first question, you need to know HOW was it administrated. That is the first question: was it IV? IM? Oral?
I guess its IV-bolus otherwise it would be very hard to calculate the Vd (volume of distribution). Vd = DOSE administrated / Concentration at the exact time it was given by IV.
You have to plot the results they give you, and by looking at it, I can say the drug follows a first-order kinetic elimination behaviour. This means that for each half-life that passes (this is specific for every drug), you lose half of the concentration you have at the moment. A zero-order kinetics means you always lose a fixed mass of drug/time, so by two half-lifes you will lose all the drug you have in the organism.
SO what you need to do, is use the formula of 1º order kinetics in order to find out, what was the blood concentration when the drug was administered (time 0).
C=Co x e ^ (-Ke . t)
What we have is the drug concentration (C) at a given time (t) but we lack the elimination constant (Ke).
This is easy to calculate: Lets consider Co as 100. Notice that 100 is not the Co that we are after (the real Co at the time where the drug was administered (time 0)), but we have to consider it in order to calculate Ke. So Co = 100 at time 0, and C = 50 at time 2.
Notice what i did: i defined time 2 as 0 and by the time we get to time 4, only 2 hours have passed:
50 = 100. e^ - (ke . 2)
ln 50 = - 2ke x ln 100
Just solve it to find out Ke.
Now after we get Ke, we can use it to calculate the concentration at the real time 0:
100 = Co. e^ - (ke . 2)
Solve it to find Co. After you find Co you can use it to calculate the Vd.
Vd = dose/Co
Vd = 2000mg/Co
Hope it helps.