Six years ago, the average of the ages of Ravi, Mohan and Govind was 32 years.  If Shyam also joins them, the average of the ages of all of them becomes 36 years. The present age of Shyam is:

30

Present average of Ravi, Mohan and Govind = 6 + 32 = 38

Total present age of Ravi, Mohan and Govind = 38 × 3 = 114 years

Present average of Ravi, Mohan, Govind and Shyam = 36

Total present age of Ravi, Mohan, Govind and Shyam = 36 × 4 = 144 years

Shyam's present age = 144 - 114 = 30 years