$In\ 2010: $
Total number of employees $ = 600$
Number of employees of skills $Q=R=S=25\% \ \ of \ \ 600 =\dfrac{25}{100}\times 600=150$
Number of employees of skill $P = 20\% \ \ of \ \ 600 =\dfrac{20}{100}\times 600= 120$
Number of employees of skill $T= 5\% \ \ of \ \ 600 =\dfrac{5}{100}\times 600 =30$
$In \ 2016:$
Total number of employees increased by $15\%$ Total number of employees $=1.15 \times 600 =690$
As there is no change in skill level of $P, Q, $ and $R$
Number of employees of skill level $P = 120$
Number of employees of skill level $Q = 150$
Number of employees of skill level $R=150$
Number of employees at skill level $S \ 40\%$ increases $ = 1.4\times 150 = 210$
Number of employees at skill level $T = 690-(120 +150+ 150 +210)= 60.$
So,the correct answer is $(C).$