How do you expand 5(2y-3)?

$10 y - 15$
To expand this expression you need to distribute the $5$ across the terms within the parenthesis"
$5 \left(2 y - 3\right) \to \left(5 \cdot 2 y\right) - \left(5 \cdot 3\right) \to 10 y - 15$