normal distribution help

#1
A worker earns $15 per hr at a plant and is told that only 2.5% of all workers make a higher wage. If the wage is assumed to be normally distributed and the standard deviation of the wage rate is $5 per hr. Is the average wage for the plant $7.50 per hr?

For only 2.5% of all workers to have higher wage than $15, the correct answer for average wage shld be $5.20 instead?

I am working backwards to retrieve the answer, using a normal distribution calculator, using 15 as the start point, 100000 as the end point.

Pls guide me whether I am working in the correct direction, and one thing is how do i manually calculate the 2.5% possibility using the formula?
 
#4
hey, can someone pls explain in clear value?
If z=(data_value-mean)/(stand_dev),
what's the data value in this sense, x? I thought x=15? If not, what's 15 then? Isnt the average wage the mean ?