The problem states that the Central location used 120 notepads.
The bar graph shows that the Central office used the most notepads. We are given that the Central office used 120 notepads. The table shows that there are an unknown number of Central departments. Let's represent the number of Central departments with $c$. For now we know that each Central department used 120/$c$ notepads.
The bar graph shows that Midtown used the same number of notepads as Downtown. The Downtown bar represents about 60% the height of the Central bar. So, Midtown used 60% of 120 = 0.60 * 120 = 72 notepads. This is not one of the options, so let's find the exact value instead of estimating.
Since Central has the tallest bar and used 120 notepads, the height of the Central bar can be set to 120. We need to find a proportion between the bars.
The Downtown bar is slightly less than 75% of the Central bar, and since the Midtown bar is of the same height as Downtown, Midtown also used less than 75% of Central's notepads. 75% of 120 = 90. Based on this, it is safe to say that Midtown used 75 notepads. However, 75 is not an option, so let's continue our calculation.
Downtown is 75. The options are 75, 30 and 25. Since the height of the Midtown bar is equal to that of the Downtown, the amount of notepads used by each office is also equal. Midtown also used 75 notepads.
According to the table, the Midtown office has 3 departments. From Step 3 we determined that the Midtown office used 75 notepads. Dividing the total notepads used by the number of departments, we have 75 notepads / 3 departments = 25 notepads/department.