If z=2.5, x=102 and x=100, what is s?

I believe the problem ask for s which is the standard deviation. We must recall that the formula for z statistic is stated as:

z = (x - x over bar) / s

Where,

z = z statistic = 2.5

x = sample value or sample score = 102

x over bar = the sample mean or sample average = 100

s = standard deviation = unknown

Rewriting the equation in terms of s:

s = (x - x over bar) / z

Substituting the given values into the equation:

s = (102 - 100) / 2.5

s = 0.8

Therefore the standard deviation s is 0.8