The equation for profit is income – cost:
 Profit = Income – Cost
 Let us say that x is the number of sold amount
  
 Profit = 9 x – (25,000 + 4 x)
 Profit = 5 x – 25,000
  
 Breakeven point occurs when Profit = 0, hence:
 5 x = 25,000
 x = 5,000
  
 The breakeven is when 5,000 people uses the income tax app