d$)$ The maximum weeks by which the project can be reduced by crashing $=7_{?}$ weeks.

Total cost of crashing the project to minimum $($or maximum weeks possible$)=$$$1,520.$

$!!$ Can someone please help explain how to find the answers to d$)$ in the most simple$/$shortest

process possible please??

$(a-c$ is given just in case that info is needed$)$

Thank you!!