This picture is too blurry for me to see the actual problem, but it looks like subtracting fractions, you just subtract the numerator (top number) from the other numbers' numerator, and the denominator stays the same, example:
6/8-2/8=4/8
If your teacher wants it in simplest form you just duvide the numerator and denominator by he same number, example
4/8 divided by 4/4=1/2