Answer is 1/10 teaspoon extra salt
Step by step
We can find the difference using subtraction
3/5 - 1/2
First find common denominator which is 10, 10 is divisible by both 5 and 2
3/5 = 6/10 (multiply 5 x 2 = 10, do the same to the numerator, 3 x 2 = 6)
1/2 = 5/10 (multiply 2 x 5 = 10, do the same to the numerator, 1 x 5 = 5)
So subtract
6/10 - 5/10 = 1/10 teaspoon extra salt