If x is the number of floor seat tickets and y is the number of balcony tickets the inequality would be:
[tex]15x + 5y \geqslant 75[/tex]
And you can just plug it in to find if it would be enough
[tex]15(3) + 5(4) \geqslant 75[/tex]
[tex]45 + 20 \geqslant 75[/tex]
[tex]65 \geqslant 75[/tex]
Since 65 is not greater than or equal to 75 you will not qualify