text: # aumentar(), diminuir(), dobro() e metade()
  def aumentar(v, v_a, f=True):
      # v == Valor
      # v_a == Valor a aumentar
      v += v_a
      if f:
          return moeda(v)
      else:
          return v
  
  
  def diminuir(v, v_d, f=True):
      # v == Valor
      # v_d == Valor a diminuir
      v -= v_d
      if f:
          return moeda(v)
      else:
          return v
  
  
  def dobro(v, f=True):
      if f:
          return moeda(v*2)
      else:
          return v*2
  
  
  def metade(v, f=True):
      if f:
          return moeda(v/2)
      else:
          return v/2
  
  
  def moeda(v):
      return f'R$ {v:.2f}'.replace('.', ',')
  