Answer:
1 teaspoon
Explanation:
First, divide 84 by 21 to find how many batches will be made:
84/21
= 4
To find how many teaspoons of salt will be used, multiply 4 by 1/4, since each batch needs 1/4 teaspoon:
4(1/4)
= 1
So, Alicia will use 1 teaspoon of salt