a) $6,3 \times 10^{9}$

Step 1 ：To solve this problem, we need to multiply 6.3 by 10 raised to the power of 9: \(6.3 \times 10^{9}\).

Step 2 ：Now, we calculate the result: \(6.3 \times 10^{9} = 6,300,000,000\).

Step 3 ：\(\boxed{6,300,000,000}\)