The first pic is an example please help me resolving the second picture. Thank you!

What is the total crashing cost? $840 (Enter your response as a whole number.) Part 1 of 6 Points: 0 of 4 per week: \begin{tabular}{cccc} \hline Activity Duration (weeks) & Precedes & Crash Cost/Week \\ \hline A (start) & 3 & B,C & $380 \\ B & 2 & E & $120 \\ C & 4 & F & $200 \\ E & 1 & F & $150 \\ F (end) & 2 & - & $450 \\ \hline \end{tabular} activity down to 0 weeks duration. \begin{tabular}{cc} \hline & EachActivityShouldbeReducedBY \\ (weeks) \end{tabular}