So we want to know what mean absolute deviation is of the prices of the 5 products. First we calculate the mean value x=(23+29+14+26+18)/5=22. Now we calculate the distance of each price and the mean value and those are v1=23-22=1, v2=29-22=7, v3=22-14=8, v4=26-22=4, v5=22-18=4. Now we take the mean value from our distances: M=(1+7+8+4+4)/5=4.8 and we got our mean absolute value.