Boron has two isotopes, boron-10 and boron-11. Boron-10 has five protons and five neutrons. How many protons and neutrons does boron-11 have? Explain.

Then the mass number is total protons plus neutrons. For boron-11 this total is 11, and five of the particles are protons, thus $11 - 5 = 6$ neutrons.