Answer: Annual Worth = Present Worth÷[PV(15%,20 yrs)]
 = -$4,852.42÷6.25933
 = (-)$775.23 
 Here, the annual worth of the given system is negative (i.e. - $775.23). 
 
The filter is not justified economically, this is because the present worth and annual worth of the system(investment) is negative,
Step-by-step explanation:
In order to calculate the annual worth, we'll first compute the existing insurance premium and new insurance premium using the following formula.
i.e. Existing Insurance premium = ($700,000÷$100)×$1.00 = $7,000 
New Insurance Premium (after installing sprinkler) = 
 = $2,880 
 Now, evaluating Savings in insurance premium.
Saving in Insurance Premium = Existing Insurance premium - New Insurance Premium 
 = $7,000 - $2,880 = $4,120 (this will be considered as annual cash flows) 
 
Given : 
Annual maintenance costs for sprinkler system = $1,700 
 Investment in Sprinkler system = $20,000 
 ∴ Net annual cash inflows = Saving in Insurance Premium - Annual maintenance costs 
 = $4,120 - $1,700 = $2,420 
Now, Present worth of the system is given as :
 Present Worth of system = [Net Annual Cash Flows×PV(15%,20 yrs)] - Investment cost 
 = ($2,420×6.25933) - $20,000 = $15,147.58 - $20,000 = (-)$4,852.42 
 Annual Worth = Present Worth÷[PV(15%,20 yrs)]
 = -$4,852.42÷6.25933
 = (-)$775.23 
 
Here, the annual worth of the given system is negative (i.e. - $775.23). 
 
2) The filter is not justified economically, this is because the present worth and annual worth of the system(investment) is negative,