It seems that you have missed the necessary options to answer this question, but anyway, hope my answer helps. The question that you ask when understanding the problem would be this: "<span>what do I want to find out?"
Since the problem seeks for an answer, this would be the correct question. Hope this helps.</span>
Answer:
7 dogs
Step-by-step explanation:
$30/3 = how many dollars per dog
$10 per dog he washes
$70/$10 = 7, he washes 7 dogs