Propose is related to Answer. Answer is related to Key. Key is related to Master. 
Number is related to System. System can be used for Efficiency. Efficiency is a synonym of Effectiveness. 
Propose <--RelatedTo--> Answer <--RelatedTo--> Key <--RelatedTo--> Master 
Number <--RelatedTo--> System --UsedFor--> Efficiency <--Synonym--> Effectiveness 