Crystal charges a flat fee of $10 plus an additional $5 per hour to babysit given the situation what is the range

We assume Crystal may be willing to babysit for a period of up to 3 months (90 days), so 90×24 = 2160 hours. Her hourly fee for that period will be ...

... (2160 hours) × ($5/hour) = $10,800

That amount added her $10 initial charge may represent the upper limit of her pay. The lower limit will be the $10 initial charge.

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Comment on the question

Since no upper limit on hours is given, we conclude the problem is not well-specified.

We can make a variety of different assumptions regarding the upper limit of babysitting time.

We might choose to consider this a daily charge, so the upper limit is $130 per day.
We might consider that Crystal is willing to babysit while the child's parents are on a 2-week vacation.
We might consider that Crystal is willing to babysit for the duration of her summer vacation from school (about 3 months). This is the assumption we use here.