Answer:
If the original recipe requires 2/3 cup of flour and 3 ¾ teaspoons of salt, we can determine the amount of salt needed for one cup of flour using a proportion.
2/3 cup flour : 3 ¾ teaspoons salt 
1 cup flour : x teaspoons salt 
We can cross-multiply to get:
(2/3) * x = (3 ¾) * 1 
2x/3 = 15/4 
Multiplying both sides by 3/2: 
x = (9/2) teaspoons of salt 
Therefore, Lexi needs 9/2 or 4.5 teaspoons of salt when making corn bread with 1 cup of flour to maintain the ratio.