A solution has a pH of 8.4. what is the H+ concentration of the solution?

A solution has a pH of 11. What is the H+ concentration of the solution? Is the solution an acid or base?

Your father goes to the store to buy cleaner to remove such deposits from your bathtub. He has a choice between a product containing lemon juice (H+ =10^-2.5M) and one containing vinegar (H+ = 10^ -3.3M) which product would you recommend he purchase and why?