To express a number in cientific notation (often refered to as scientific form), we take the first digit and then put a decimal right after it. Next we take a count of all other numbers after the first digit and that would determine the value of the index (exponent).
In this case, we hould have 9, followed by a decimal, and then followed by 18 numbers. Note that any number aside zero would be written down after the first digit. Any zero would be disregarded.
Hence;
[tex]\begin{gathered} 9,150,000,000,000,000,000 \\ In\text{ scientific notation becomes;} \\ 9.15\times10^{18} \end{gathered}[/tex]