What would the mean be?

Question

Person A has a z-score of -3 and is on her phone for 7 hours a day. Person B has a z-score of -4 and is on her phone for 3 hours a day. It is a normal distribution. What would be the mean of the data? (checking my answer)

Answer 1

From equations

A: -3 = (7-μ)/σ

B: -4 = (3-μ)/σ

 

I got standard deviation 4 and std. dev. μ = 19.  Is this the same work & answer that you did?