As number it is: 1,500,000,000
To write 15 billion in standard form, you express it as a number multiplied by a power of ten. Since 15 billion is 15 followed by 9 zeros, it can be written as ( 1.5 \times 10^{10} ).
As a number it is: 24,600,000,000 = 24.6 billion
19.35 billion = 19,350,000,000
As a number: 7,125,000,000 = 7.125 billion
As a number it is: 1,800,000,000 = 1.8 billion
15,000,000,000
Since you asked how I would write the number, the answer is 1031.
19.35 billion = 19,350,000,000
As a number: 7,125,000,000 = 7.125 billion
As a number it is 12,800,000,000 = 12.8 billion
As a number it is: 6,080,000,000 = 6.08 billion
As a number it is: 24,600,000,000 = 24.6 billion
As a number it is: 529,600,000,000 = 529.6 billion
As a number it is: 1,800,000,000 = 1.8 billion
15,000,027
15,000,000,000
80 billion = 80,000,000,000