Let the number of executive class air ticket sold is x and economy class ticket sold is y.

Given seating capacity of aeroplane is maximum 200

So x + y <= 200

Again given at least 20 tickets for executive class are reserved

i.e.  x>=20

Again given number of tickets of economy class should be at least 4 times that of executive class

So y > = 4x

Profit on sale on x ticket on executive class and y class on economy class is

    Z = 100x + 600y

Now LPP problem is

Maximize Z = 100x + 600y   ............1 

Subject to constraints

       x + y < = 200  ................2

      x > = 20 ..........................3

      y > = 4x ..........................4

      x >= 0, y >= 4 ................5

Now plot equation 1 to 5, as shown in figure.

Now the shaded region is the feasible region which is bounded by point A, B and C.

  Point                 Z = 100x + 600y

A(20, 80)             68000

B(40, 600)           136000

C(20, 180)           128000

Now the maximum profit of rupees 136000 will be earned by selling 40 executive class tickets and 160 economy class tickets.