Garages or shops where automobiles or other motor vehicles are repaired, painted, trimmed, or welded for the public shall pay the following license taxes: Each shop where the work is done by one man, $5; each shop where the work is done by two men, $10; each shop where the work is done by more than two men shall pay a license of $10, and an additional license of $5 for each workman in excess of two so employed. Where garage or shop owners do work in shops they shall be counted as workmen. The maximum number of men employed at any time during the license year shall be the basis of computing the license due.