Answer
$\mathrm{COP}_{\mathrm{R}, \max }=2.64$
Work Step by Step
The maximum COP that this refrigeration system can have is
$$
\mathrm{COP}_{\mathrm{R}, \max }=\left(1-\frac{T_0}{T_s}\right)\left(\frac{T_L}{T_0-T_L}\right)=\left(1-\frac{298 \mathrm{~K}}{393 \mathrm{~K}}\right)\left(\frac{273}{298-273}\right)=\mathbf{2 . 6 4}
$$
