Kodak T-Max 400 is a medium-speed black-and-white film stock that has a more modern formulation than Tri-X which provides slightly higher sharpness and finer grain. T-Max 400 is a great general-purpose film, and the choice between T-Max and Tri-X comes down to personal preference. 
 
Each roll of 35mm T-Max 400 has 36 exposures.