A stock solution is prepared by adding 26 mL of 1.1 M K3PO4 to enough water to make 30 mL. How many moles of K+ are in 21 mL of the stock solution?

How many moles to prepare the 30 mL? That is M x L = ?? moles K3PO4.

How many mols are in the 21 mL? That will be ?? moles x (21/30) = xx moles.
How many K^+ there. Just 3 x that amount.