In a diluted solution of coke(1.00mL of regular coke and diluted to the mark of a 25.00mL flask), the concentration of phosphate is 5.13 x 10^-5 mols/L.

What is the concentration of phosphate in an original coke?

What is the concentration of phosphoric acid in an original coke?

1. Find the amount of moles of phosphate in the 25.00 mL of diluted coke using the concentration you have.

That amount of moles were originally present in 1.00 mL of coke. Now, calculate another concentration, using the same amount of moles you got previously, and the new volume.

2. Write an equation for that: H_3PO_4 \rightleftharpoons 3H^+ + PO_4^{3-}

With that, you should be able to do the second part. :)