The total number of neutrons in an atom of lithium-7 (⁷Li) can be determined by subtracting the atomic number (number of protons) from the mass number (total number of protons and neutrons):

Mass number = 7

Atomic number = 3 (lithium)

Number of neutrons = Mass number - Atomic number

= 7 - 3

= 4

Therefore, there are 4 neutrons in an atom of ⁷Li.