SCAN disk scheduling alorithm scans down towards the nearest end and then when it hits the bottom it scans up servicing the requests that it didn't get going down.
So, Requests are serviced in order : $20, 22, 38, 40, 10 ,6 , 2$
So, total disk movements $ = | 20- 20 | + | 20 -22 | + |22 - 38 | + |38 - 40| + |40 - 10| + |10 - 6| + |6-2|$
$\Rightarrow 0 + 2 + 16 + 2 + 30 + 4 + 4 = 58$
And each disk movement takes $6ms$. So, total Seek time $ = 58*6 = 348ms$