The mean absolute deviation is the mean of the absolute values of the differences of the numbers from their mean. It is convenient to let a spreadsheet or calculator do the tedious math. Here it is by hand:
Total of given values: 135
Mean of given values: 135/6 = 22.5
Deviations of given values from the mean:
... {2.5, 1.5, 2.5, 0.5, -2.5, -4.5}
Absolute values of deviations from the mean:
... {2.5, 1.5, 2.5, 0.5, 2.5, 4.5}
Total of those: 14
Mean absolute deviation: 14/6 = 2 1/3.