Final answer:
The answer can be written as 1.1E11.
Step-by-step explanation:
The product of multiplying 4.5E6 by 2.51E7 is 113,295,000,000. However, when considering significant figures, the answer can only have the same number of significant figures as the value with the fewest significant figures. In this case, 4.5E6 has two significant figures, so the answer should be rounded to two significant figures as well. Therefore, the answer can be written as 1.1E11.