Three activities are candidates for crashing on a project network for a large computer installation (all are, of course, critical). activity details are in the following table: activity normal time (days) crash time (days) normal cost total cost with crashing immediate predecessor(s) a 77 66 $ 4 , 500$4,500 $ 5 , 100$5,100 long dash— b 44 22 $ 1 , 200$1,200 $ 3 , 100$3,100 a c 1111 99 $ 4 , 000$4,000 $ 6 , 400$6,400 b activity that should be crashed first to reduce the project duration by 1 day is