Answer: substantial
Step-by-step explanation:
From the question, we are informed that Greta is concerned that one of the potential market segments she has identified for her dog grooming service is too small and has too little income to have sufficient buying power.
The above analysis shows that Greta is concerned with whether the substantial segment. A segment is said to be substantial when the said segment is big and therefore should be worth targeting and the members of this particular segment should have buying power.