Final answer:
The screen result of 9e+10 means that the total square footage of the forests is approximately 900,000,000,000.
Step-by-step explanation:
When Ivanna used her phone to calculate the square footage of the U.S. national forests, her screen displayed the result as 9e+10. This is scientific notation, which is a way to represent very large or very small numbers using powers of 10. The 'e+10' in 9e+10 means that the decimal point should be moved 10 places to the right, resulting in a number that is approximately 9 followed by 10 zeros. So, the screen result of 9e+10 means that the total square footage of the forests is approximately 9 with 10 zeros after it, or 900,000,000,000.