MathNet 2023-part-03 — 191 problems (EN–VI) Question 145

Consider the expression $E=\frac{3(x+y)(z+t)}{8} \cdot\left(\frac{1}{x y}+\frac{1}{z t}\right)$, where $x, y, z, t \in[1 ; 3]$. Determine the largest and the smallest possible values of the expression $E$.