1. The problem is to understand the number 3.91938417383707E-28. 2. This number is written in scientific notation, where "E-28" means \times 10^{-28}. 3. So, 3.91938417383707E-28 = 3.91938417383707 \times 10^{-28}. 4. This is a very small number, close to zero, because it is multiplied by 10 raised to a very large negative power. 5. Scientific notation is used to express very large or very small numbers in a compact form. 6. The number 3.91938417383707E-28 is approximately 0.0000000000000000000000000000391938417383707. 7. In summary, 3.91938417383707E-28 is a tiny decimal number represented in scientific notation.