PTA calculation

 Guys pls help

A contractor has agreed to build a storage depot for a target price of $90,000, but there is some uncertainty involved in the project, so buyer & seller have agreed that the ceiling price will be $100,000. The buyer will pay 100% costs  upto $80, 000 and 75% of costs between $80,000 & $100,000 but any cost over $100,000 is absorbed by the contractor. What is the point of total assumption for this contract for the buyer?

1. $100, 000

2. $90, 000

3. $87, 750.25

4. $93, 333.33

 

Ans: option 4.. how?

 

Target price = 90,000
Ceiling price = 100,000
As the builder said his ratio is 100 % for costs upto 80,000 that means
Cost price = 80000

After that buyer :seller ration = 75:25

So PTA = {( 100000-90000)/buyer's ratio }+ 80000 = 93333.33

let me know

 if the buyer pays 100% of the cost upto $80, 000 then buyer ratio will be 80% to the ceiling price right. How come 75%. Please explain.

 The buyer agreed to pay 100% up to 80,000 so the buyer and seller agreed to  the target  cost will be 80,000 which is a 75:25 (?)