can anyone tell me how to find the p values for a z-score of 1.38 using the formula
_
x - score
variance/squareroot n
That's correct if you have a greater than sign in the alternative hypothesis.
This cannot be answered until I know $\displaystyle H_a$.
It doesn't matter if we are testing a mean or a proportion, we need $\displaystyle H_a$.
AND if $\displaystyle H_a:\mu\ne 21$, then the p-value is twice this 0.0838.