$\dfrac{2021 \times 13 + 2007 + 2020 \times 2007}{2020 + 2020 \times 250 + 1500 \times 2020}$
$=\dfrac{2007 \times (2020 + 1) + 2021 \times 13}{2020 \times (1+250 + 1500)}$
$= \dfrac{2007 \times 2021 + 2021 \times 13}{2020 \times 1751}$
$= \dfrac{2021 \times (2007 + 13)}{2020 \times 1751}$
$= \dfrac{2021 \times 2020}{2020 \times 1751}$
$= \dfrac{2021}{1751}$