μ−3σ is 3 standard deviations to the left of the mean

μ+σ is 1 standard deviation to the right of the mean

P( -3 < z < 1) = P( z < 1) - P( z < -3) = 0.8413 - 0.0013 = 0.8400

P(μ−3σ≤x≤μ+σ) = 0.997/2 + 0.68/2 = ...

P(μ−3σ≤x≤μ+σ) = P(-3< Z< 1) = P(z< 1) - P(z< -3)

Using this table

https://www.stat.tamu.edu/~lzhou/stat302/standardn...

P(z< 1) = 0.84134

P(z< -3) = 0.00135

P(μ−3σ≤x≤μ+σ) = 0.84134 - 0.00135 = 0.83999

so if you only had a 4 digit table 0.8413 -0.0014 = 0.8399

Why are you asking this now, as opposed to Friday?