we are given 
that a 11.630 g milk chocolate bar contains 7.815 g of sugar
so, 
total amount = 11.630g
sugar=7.815g
now, we can find 
the percentage of sugar present is ((sugar)/(total amount))*100
now, we can plug values
the percentage of sugar present is

now, we can simplify it 
we get 
So, the percentage of sugar present is 67.20%..........Answer