There are 10 zeroes in the number 780 billion without using decimals. It appears like this when written out, 780,000,000,000.
3.5 billion is written as 3,500,000,000, so there are a total of 8 zeros. 1 billion will always have 9 zeros, so to write a number out digits you would just have to move the decimal point over 9 places. When you move the decimal 9 places to the right in 3.5 billion, you'll get your answer of 3,500,000,000 and you can simply count the zeros.
There are 9 zeros in one billion
A billion is 1 followed by nine zeros 70 billion thus has 10 zeros 70,000,000,000
Seven zeros.
9 zeros