Yes, I need to adjust timing for accommodations

I interpreted the city's investment in computer technology as NECESSARY for the increase in rush hour traffic flow, so I mapped it like this: ~increase in traffic -> ~ invest in tech (contrapositive: invest in tech -> increase in traffic) I similarly mapped the next one thinking that the increase in traffic flow was NECESSARY for the resolution of the predicament so I mapped it like this: ~ resolution -> ~ increase in traffic (contrapositive: increase in traffic -> resolution). I chained it together so it became invest in tech -> increase in traffic -> resolution (contrapositive ~ resolution -> ~ increase in traffic -> ~ invest in tech). I chose B because I interpreted investment in tech as necessary for the resolution (~resolution -> ~invest in tech; invest in tech -> resolution) - this maps out onto the chain I created. As in the explanation video, I interpreted the sentences as conditionals:  If the city hadn’t invested in computer modeling technology last year, this traffic flow wouldn’t have increased; If this traffic flow hadn’t increased, the city’s financial predicament wouldn’t have been resolved. 

I understand “if” triggers sufficient condition but I do not understand conceptually how the investment in computer technology was sufficient for the increase in traffic flow or the increase in traffic flow was sufficient for financial resolution. For some reason it seems necessary for me? 

I watched the explanation video and am still having a hard time.