Let X represent the number of nickels Sofia has.
Sofia has (X + 2) number of quarters.
Sofia has (2X + 5) number of dimes.
Since a quarter equals 5 nickels, (X + 2) quarters equals (5X + 10) nickels.
A dime equals 2 nickels, so (2X + 5) dimes equals (4X + 10) nickels.
Therefore, Sofia has (10X + 20) nickels worth, which equals 350¢.
Therefore, X = 5, and Sofia has 5 nickels.