How to create plugin to change the field dynamically based on another entity field value ?

Hi all,

I am new to plugin crm

I have two Entities - [ WorkOrder and Agreement ]

Workorder [Priority-Lookup]. It contains Name,Level Fields-[optionset-1,2,..10]

Agreement [missed visit,sla penalty] -[currency,currency]

Requirementis i have toupdate workorder priority based on the penalty value dynamically

Suppose there are list of agreements that have penalty value as [100,200,300,400..]-{Dynamically given by user}

Based on that i have to update the priority of the workorder i mean if penalty largest value is 1000 then that should be a highest priority workorder ..Likewise if penalty is 999 then that should have priority as 2..

Please give me some idea on this friends...

Thanks

Maanasa Gutha