The feasible region of the linear programming problem is represented below: The constraints of this LPP are

Look at the straight line that cuts at $(0,50)$(0,50) and $(50,0)$(50,0).

The equation of the line is $x+y=50$x+y=50.

The feasible region (shaded region) includes the line and the part above it.

Hence, the constraint it $x+y \geq 50$x+y≥50.

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Now, look at the dashed line which cuts at $(0,90)$(0,90) and $(90,0)$(90,0).

The dashed line has the equation $x+y = 90$x+y=90.

If it is dashed, the line is not included in the feasible region i.e $(0,90)$(0,90) and $(90,0)$(90,0) are not part of the feasible region.

The shaded region is below this line.

Hence, the constraint is $x+y<90$x+y<90.

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Hence, option 4 is the answer.