Bheja Fry question

I came across this Bheja Fry question on internet.

Question 

If    1  +   3    =   4

       2  +  4   = 10

        3  +  5  =  18

Then   4  +  6   = ???

Answer 

       1  +  3  =  4  (  given  )

       2  + 4   = 6 but 10  (  given  )

       3  +  5  =  8  but 18  (  given  )

       

If we see the differences between the actual and given answers,  we can say that each time the difference is getting increased by  6 , 8........

If we follow the  same pattern, the next difference should be   10.

==>>   4  +  6  =  28  actually it is 10 

So 1 + 3 =  4

      2 + 4  =  10

       3 + 5  =  18

        4  +  6  =   28