Answer: d) 3 hours.
Step-by-step explanation:
Let x be the required number of hours for which the total fee charged by the companies the same.
Given: Peppy Pets charges a flat fee of $15 plus $3 per hour .
So Total charge = 15+3x ( in dollars)
Happy Hounds charges a flat fee of $21 plus $1 per hour.
So Total charge = 21+x ( in dollars)
When the total charge for both companies are the same, then
Hence, the correct option is d) 3 hours.