The answer for your problem is 192
The mean deviation of the ratings is 4.12
<em><u>Explanation</u></em>
The ratings of the ten experts are: 34, 35, 41, 28, 26, 29, 32, 36, 38 and 40
So, the mean of all ratings 
<u>The formula for Mean deviation</u>
, where
is the given data from
to
,
is the mean of the data and
is the total number of data. So.....

So, the Mean deviation 
Here, y = -15 with x = -20
LCM of 15 & 20 is 60, so divide 15 & 20 from 60,
60/15 = 4 & 60/20 = 3
Now, multiply the results with intial values,
4y = 3x
y = 3/4 x
When y = 12,
x = 12 * 4/3
x = 48 / 3
x = 16
In short, Your Answer would be 16
Hope this helps!