John Gill Commentary Numbers 3:22

"Those that were numbered of them, according to the number of all the males, from a month old and upward, even those that were numbered of them were seven thousand and five hundred." — Numbers 3:22 (ASV)

Those that were numbered of them Of the two families that sprung from Gershon: according to the number of all the males, from a month old and upwards : in the said families; [even] those that were numbered of them, [were] seven thousand and five hundred ; 7,500 men, which was neither the least nor the largest number of the sons of Levi.