Tony misplaced 7 77 stamps from his collection. he knows that each stamp of his is worth $ 0 . 1 5 $0.15dollar sign, 0, point, 15 and that the total value of them is now only $ 5 . 5 5 $5.55dollar sign, 5, point, 55.

I take it that only 7 stamps are misplaced and that we are asked for the total value of the stamps including those which have been misplaced. 
If each is worth $0.15 then, the total worth of 7 stamps is $1.05. Then, we add this value to the value of his remaining stamps, $5.55, the answer would be $6.60.