In this question, we need to calculate  Z1 and Z2.  Therefore, Z1 =70-40/10, which is equal to 3. The z value of 3 is 0.015.

Similarly, the value of Z2 is 70-100/10 which is equal to -3. Thus, the value of z is 0.015

And so, Z1+Z2 is equal to 0.3%. But how do  we interpret this value? Please see the solution/answer #5 slide for its interpretation.