How can you determine the number of protons and neutrons in an isotope when given the symbol and mass number?

When given the symbol, you can look on the periodic table of elements to find what the atomic number is, which is the number in the corner next to the symbol. The number of protons in the element is the atomic number. The number of neutrons is the mass number minus the number of protons.
Hope it helps:)

They can measure  the amount of energy gained or lost