I am attempting to find an unknown value given the probability of the range of X. I am unsure of how to calculate the value given the added constants defined in the problem and which values I need to use to look up the z-scores to plug into the x = z + $\mu (\sigma )$. I have found z given probability of 0.95 to be 1.644853. Not really sure if that is the correct value to use or how to go from here? Here is the problem:

A random variable X has the distribution $N(1500,(200{)}^{2})$. Find B, where $P(1500-B<X<1500+B)=0.95$

A random variable X has the distribution $N(1500,(200{)}^{2})$. Find B, where $P(1500-B<X<1500+B)=0.95$