Answer 1

The given function is p = `183 + 120 D – 3D^2` 

∴ `(dp)/(dD)=120-6D` 

Now `(dp)/(dD)`=`0⇒120-6D=0⇒D=20` 

For increasing the price 

`(dp)/(dD)>0` 

`120-6D>0` 

`-6D>-120` 

`D<120/6` 

`D<20` 

Demand and price cannot be negative
∴ Price is increasing in the internal (0, 20).