calculate the molarity of k+ in a soln prepared by adding .2L of .200M K3PO4 and 75.0mL of .5M K3PO4. assume volumes are additive.

A few of steps here and more than one way to answer the problem

You need to calculate the total number of moles of K3PO4 from the two volumes and two concentrations.

This is in the total volume of 0.2 L+0.075 L=

You can now calculate the molarity of K3PO4 in moles/L

Assume that the K3PO4 dissociates to

3K^+ and PO4^3-

you can now calculate the [K+]

Tip - try not to forget the leading zeros as I nearly read 2 L rather than 0.2 L 8-))