Find the z-scores that bound the middle 74% of the area under the standard normal curve.

Since 74% of the middle area is bounded, this means that there is 13% on the left side, and another 13% on the right side.

P (left) = 0.13

P (right) = 1 - 0.13 = 0.87

At this P values, the z scores are approximately:

z score (left) = - 2.22

z score (right) = 1.13