To obtain this answer, we need to use the means command to produce the average or mean value of the variable incmon. In addition, we need to type a qualifier, which will restrict which observations are to be included in the calculation.
To do this, let's type the following command:
means incmon if age > 40 & age~=.
The above command produces the following table:
Variable | Type Obs Mean [95% Conf. Interval]
-------------+----------------------------------------------------------
incmon | Arithmetic 163 1426.859 1152.709 1701.009
| Geometric 156 785.4031 647.9911 951.9545
| Harmonic 156 351.8236 263.5576 528.9802
------------------------------------------------------------------------
From the table, we can see that the average or mean monthly pay is 1,427 rand.