By setting up an equation accounting for the flat rate and hourly wage Kelsey receives for babysitting, it can be concluded that she worked 4 hours to earn $16.
To determine how many hours Kelsey babysat to earn $16 when she earns a flat rate of $10 plus $1.50 per hour, you can set up an equation based on the information given. You subtract the flat rate from the total earnings to find the amount earned from the hourly rate alone. Then, you divide this amount by the hourly rate. So, if Kelsey earned $16 in total and the flat rate is $10, then she earned $16 - $10 = $6 from the hourly rate. The hourly rate is $1.50, so you divide the hourly earnings by the hourly rate: $6 / $1.50 = 4. Therefore, Kelsey babysat for 4 hours.
So answer is: Kelsey babysat for 4 hours to earn $16.
Conclusion: Using a simple algebraic approach, it is determined that Kelsey babysat for 4 hours to make a total of $16.