1.2000,000,000
I would write it as 9.5*10^12 but you can write it out, in full, as 9,500,000,000,000.
Sixteen point two billion is how I would write it.
5 billion 6 million 12 = 5,006,000,012
Since you asked how I would write the number, the answer is 1031.
3.87 x10^12
1,200,000,000
You would write it as 125,000,000,000
To write 87 billion 932, you would start by writing the number 87, followed by the word "billion." Then, you would write the number 932 as digits. So, it would be written as "87 billion 932."
You would write it as 20,750,000,000. Twenty billion, seven hundred fifty million.
6.9 billion as a number would be 6,900,000,000. To write it out without digits it would be six billion and nine hundred million.
Exactly as in the question: 1.351 billion.
I would write it as in the question.