how do i get this?

Data on a project consisting of 5 activities is given in the table below. The project network has been drawn with the earliest start, earliest finish, latest start, and latest finish for each activity computed. Normal Crash Activity Time Normal Crash Immediate Time Cost Cost Predecessors (Days) (Days) A 6 5 $1000 $1800 B 8 6 $500 $1600 $900 $1700 4 3 D 5 3 $800 $1900 E 8 8 5 $900 $2400 D A 151 117 6118 DO TI Q 010 START 010 - 12112 END 12112 112 Ore CI 04 4112 412 What is the minimum additional cost to reduce the project completion by 4 days. Please specify the amount as a number without a dollar sign. e.g. 1750