Hey vinu !

the answer is wrong . This is because the 2 small sectors u considered are not sectors .their length is varying . See ,you hav assumed the part of small sector cutting the hexagon equal to 10 . But infact  , it is not 10 . If you see the triangle formed inside the hexagon , sum of two sides is equal to 3rd side , which is not possible (40+10=50) . 

Pls check and reply !!!!!!