<u>Answer:</u> The number of bottles that will be needed are 6
<u>Explanation:</u>
We are given:
Amount of solution, the intern is asked to prepare = 3 L = 3000 mL (Conversion factor: 1 L = 1000 mL)
Strength of solution needed = 30 % (w/v)
This means that in 100 mL of solution, the solute present is 30 grams
So, in 3000 mL of solution, the solute present will be = 
Active ingredient present in 1 bottle = 8 ounce of 70 % (w/v)
<u>Conversion factor used:</u> 1 ounce = 29.57 mL
So, 
Amount of active ingredient present in 1 bottle = 
To calculate the number of bottles, we need to divide the total amount of solution needed by the amount of active ingredient present in 1 bottle, we get:

Putting values in above equation, we get:

Hence, the number of bottles that will be needed are 6