Answer: 105 sandwiches can be made from all the peanut butter.
Explanation:
Given: Total jars of peanut butter = 21
Part of peanut butter required for each sandwich =

Total number of sandwiches made = ( Total jars of peanut butter ) ÷ (Part of peanut butter required for each sandwich)

Hence, 105 sandwiches can be made from all the peanut butter.