A pet food manufacturer has a facility with two lines that blend, cook, and cancat food. The production manager is curious whether there is a difference in the population mean amount produced by the lines. The manager randomly picks 100 daily production reports, 37 of which were for one production line and 63 of which were for the other. Assuming the population variances are equal and using the pooled estimate of the standard deviation, a hypothesis test for the difference between the two population means would have how many degrees of freedom?

DF = ...