Chapter 13.4, Problem 84E

To determine

To calculate: The number of article to the nearest $1000$ articles written by researchers in U.S from $1983\text{ to 2003}$ if the Journal published in Physical review written by researchers in U.S during the same period is given as $U\left(t\right)=\frac{4.6e^{0.6t}}{0.4+e^{0.6t}}$ thousand articles per year where $t$ is times in year $\left(0\le t\le 20\right)$.