Answer:
The revenue is maximum around 187.5 that means we can sell 187 or 188 calculators to get the maximum revenue.
Explanation:
Let the total number of calculators sold = x
The price per demand of calculator , p =150 - 0.4x
Total revenue =

=

To maximize revenue, derivative of total revenue must be zero.
= 0
150 - 0.4x - 0.4x = 0
150 - 0.8x = 0
0.8x = 150
x = 187.5
So the revenue is maximum around 187.5 that means we can sell 187 or 188 calculators to get the maximum revenue.
Maximum revenue =

=14,062.4