Answer:
2 cups of sugar
Explanation:
Trina uses the number of cups of sugar in a recipe = 
 
 = 0.5 cups
she uses the number of cups of flour in a recipe = 
 
 = 0.75 cups
The proportion of sugar and flour she uses = 

Let the sugar would be needed for 3 cups of flour = x 
Therefore, 
 × 

 

x = 2
She would be needed 2 cups of sugar.