$\frac{2}{10},\frac{n}{45}$ is interpreted as:

$2\%$ cash discount if the whole amount is paid within $10$ days, the balance is due in $45$ days.

$10\%$ cash discount if the whole amount is paid within $2$ days, the balance is due in $45$ days.

$45\%$ discount if paid within $2$ days.

$2\%$ discount if paid within $45$ days.