If a student scored 92 on a test where the mean score was 78.4 and the standard deviation was 4.3 the student z score is?

3.1627907

Work:
The formula for calculating z scores is 
(given value) - (average value)

        (standard deviation)

You plug in the given values from the question, which gives you
(92) - (78.4)

      (4.3)

Solving that expression in a calculator gives you the value 3.1627907. This is your z score.