Answer:
12 days
Step-by-step explanation:
As, After 4 days, remaining chairs = 480
So, the number of chairs already installed = 720-480 = 240
In 4 days they constructed = 240
In 1 day =240/4 = 60
So in 1 day = 60
So in "x" day = 720
So = 720/60
= 12
= 12 days