You write one billion two hundred thousand as 1,200,000. It's as simple as that. Just put a comma after every three digits to separate the thousands, millions, billions, and so on. Easy peasy lemon squeezy.
11,100,003,000
150,008,001,500
126,000,000,000 is One hundred and twenty six thousand million (or one hundred and twenty six billion).
6,000,401,006.003
Expressed in words, this is two hundred one billion seven hundred thousand five.
111111111100
110,300,000
60,700,100,312
ten billion six hundred eighty-six million one hundred thousand
Two billion, thirty million, one hundred four thousand = 2,030,104,000
176,000,000,000,000
1000000800
1,000,400,000
150,008,001,500
150,008,001,500
701,402,002,004
Nineteen billion four hundred seven million one hundred thirty-four thousand is 19,407,134,000