what amount of water is needed!? can you please answer everything asked in the question:)

2. Now you need to prepare a different buffer: 2.000L of 2.00M phosphate buffer, pH 7.40. You have the following reagents available to you. ( PKas for phosphoric acid are: 2.14,7.20, and 12.40) a. From the table above, select the combination of reagents that you will use for your buffer. (Note: there are several possibilities - you just need to choose one.) (1) b. Calculate how much of each reagent (and water) you will use to make this buffer