The easy way is to write this number in part as they are mentioned
The first part says five hundred million or 500 million
which can we written as 500 X 1,000,000(million has 6 zeroes)
So that would make it 500,000,000
the second part says one hundred and fifteen or 115
Lets add these two value
500,000,000+115 = 500,000,115
So this would be our standard form