Answer: B (2/3 tsp)
Explanation:
Set equal to each other to look for x.
3/4 cups sugar per 1/2tsp salt is (3/4)/(1/2) and we are looking for 1 cup sugar. Therefore:

Cross multiply. You should get:

Divide both sides by 3/4.

Simplify
x=2/3
So you will use 2/3 tsp salt for every 1 cup sugar.