Answer:
Juan has to work at least 21 weeks.
Step-by-step explanation:
Juan earns $3 a day, then he earns $21 per week.
Let x be the number of weeks Juan works. He will earn $21x in x weeks.
Juan has saved $213,
He earns $21x,
Juan's total earnings are $213+$21x.
He needs to save at least $654, so
Juan has to work at least 21 weeks.