Question 160719
size (sq.ft):1500,1900
cost        :$20 000,$24 000
(24,000-20,000)/(1900-1500)
4000/400=$10 per ft^2 
(2,300-1,900)*10+24,000
400+10+24,000
4,000+24,000=$28,000  for the 2,300 ft house.