To determine how many horses can be trained with the given information, we start by noting that the trainer needs 5 treats per training session and has a total of 42 mints.
The correct equation to represent the number of horses \( h \) that can be trained based on the available mints would be:
\[ 5h = 42 \]
To find \( h \):
\[ h = \frac{42}{5} \] \[ h = 8.4 \]
Since the trainer cannot train a fraction of a horse, the number of horses that can be trained must be a whole number. Therefore, \( h = 8.4 \) is not a viable solution.
Thus, the correct response is:
5h=42, so h=8.4 horses, which is not viable.