Null Hypothesis, need help with it.

THE NULL VS ALTERNATIVE LECTURE WASNT CLEAR AT ALL, I  STILL CAN'T WORK MY WAY TO MAKING PROPER SELECTION OF THE NULL HYPOTHESIS.

- IS IT DIFFRENT FOR ONE TAILED AND TWO TAILED TEST?
- IN THE SECOND EXAMPLE , SALARY IS MORE THAN (NOT INCLUSIVE OF) $125,000. THE CLAIM IS "SALARY > $125,000" .THE NULL HYPOTHESIS THUS SHOULD HAVE BEEN SALARY <= $125,000  AND ALTERNATIVE HYPOTHESIS SHOULD HAVE BEEN SALARY > 125,000.

THE SOLUTION IN THE ASSIGNMENT SECTION ISNT CLEAR AT ALL. PLEASE DIRECT ME TOWARDS THE CONCEPT, WITH MORE CLARITY.

THANK YOU.