Study the following table carefully to answer the given questions.

In the years 2010 and 2011 together, the average number of books bought by each buyer through offline mode was 5. If $3 \over 5$th of the number of buyers buying books through offline mode, during the years 2010 and 2011 together were of the age group more than or equal to 30 years, then how many buyers were less than 30 years of age ?