John Gill Commentary Numbers 2:15

"And his host, and those that were numbered of them, were forty and five thousand and six hundred and fifty." — Numbers 2:15 (ASV)

And his host
That is, the host of Gad, as distinct from those of Reuben and Simeon, which together formed the camp;

and those that were numbered of them, [were] forty and five thousand
and six hundred and fifty .
] 45,650 men; see (Numbers 1:25) .