Weak polyprotic acids are normally

added to Coca Cola to lower its pH
to about 2.5 and impart tartness?
Show that a two litter cocacola
bottled drink that contains 0.057 to
0.084 percent of 75 percent of
phosphoric acid by mass,meets this
ph requirement.
Pka1= 2.12

I would take the average of 0.084 and 0.057 and see if that gets close to pH = 2.5.

Avg = about 0.07% = 0.007g/100g
mols H3PO4 = 0.07/98 = about about 7E-4 and that in 0.1L (if density is about 1.0) that makes 7E-3M
Then H3PO4 ==> H^+ + H2PO4^-
I.....7E-3......0.......0
C......-x......x........x
E....7E-3-x....x.........x

Solve for x and convert to pH. I obtained approximately 2.2 which is in the ball park.