It is given that Zelly works 20 hours a week at a food market for 7.50 an hour she takes home 6.75 an hour after deductions.
Therefore, the difference between the gross salary and the deducted salary is:
7.5-6.75=0.75
The rate of deduction can be calculated by dividing this difference from the gross salary as:
\frac{0.75}{7.5}=0.1
Now, we know that 0.1 can be rewritten as 10%. Therefore, the required rate of deduction for Zelly is 10%.