Let be "x" the number of hours of your work week you spend stocking shelves.
According to the information provided in the exercise, you work a total of 20 hours each week and you spend 3/5 of that time stocking shelves.
You can write that fraction as a decimal number by dividing the numerator by de denominator:

Then, to find the value of "x", you only need to multiply the total hours you work each week by 0.6.
Therefore, the result is:

You spend 12 hours of your work week stocking shelves.