X= number of tickets sold
Each ticket= $4
Total cost of dance= $400
Then
Dance committee earns = 72 + 4•X
And should be bigger than $400
Then inequality here is
72 + 4X ≥ 400
whose solution is
4X ≥ 400 - 72
X ≥ 328/4
X ≥ 82
Then answer is
Dance committee should sell, at least, 82 tickets.