budget/app/models/member.rb

class Member < ApplicationRecord
  has_many :incomes

  def income
    incomes.sum(&:amount)
  end

  def included_income
    incomes.where(included: true).sum(&:amount)
  end

  def others_included_income
    Income.where(included: true) - included_income
  end

  def burden_percent
    (Income.total - others_included_income) / Income.total
  end

  def burden_amount
    burden_percent * Expense.total
  end
end