Given 2.50x + 3.50y < 30.
Where x represent the number of hamburgers and y represent the number of cheeseburgers.
Now question is to find the maximum value of hamburgers Ben could have sold when he has sold 4 cheeseburgers.
So, first step is to plug in y=4 in the given inequality. So,
2.50x+3.50(4)<30
2.50x+14 <30
2.50x<30- 14 Subtracting 14 from each sides.
2.50x< 16
Dividing each sides by 2.50.
x<6.4
Now x being number of hamburgers must be an integer , so tha maximum value of x can be 6,
thus x = 6 hamburgers
So, the maximum value of hamburgers Ben could have sold is 6*2.5=$15
Hope this helps!!