writing and reading files with ruby

CSV.rb

require 'CSV'
  day_cost = {}
  CSV.foreach('hello.csv', headers: true) do |row|
    day_cost[row[0]] = row[1]
  end
  
  def hourly_wage(wage)
     wage.tr('$', '').to_f / 10
  end
  
  day_cost.each do |key, val|
    File.open('report.txt', 'a') do |file|
      file.write("On #{key} I spent #{hourly_wage(val)} per hour \n")
    end
  end