Could someone help me solve these problems?

1. We mix 400 ml HNO3 solution with a pH of 2 with 400 ml HNO3 solution with a pH of 1. What is the pH of the final solution?

What is the pH of an aqueous solution containing 2,52 mg KOH dissolved in 400 ml of solution?

Following the reaction between a 1.25M NaOH solution with a 1.665M H3PO4 solution we obtain 1L of solution with a pH of 11. Indicate which of the following statements are true or false:
a. The initial volume of the NaOH solution is 400ml
b. 1 mole of NaOH is involved in the reaction
c. 300 ml H3PO4 solution are involved in the reaction
d. There are 5.6 moles of NaOH in the final solution
e. The salt concentration in the final solution is 0.333M