text: const calculateTip = (total, tipPercent = .25) => total + (total * tipPercent)
  
  const fahrenheitToCelsius = (temp) => {
      return (temp - 32) / 1.8
  }
  
  const celsiusToFahrenheit = (temp) => {
      return (temp * 1.8) + 32
  }
  
  const add = (a, b) => {
      return new Promise((resolve, reject) => {
          setTimeout(() => {
              if (a < 0 || b < 0) {
                  return reject('Numbers must be non-negative')
              }
  
              resolve(a + b)
          }, 2000)
      })
  }
  
  module.exports = {
      calculateTip,
      fahrenheitToCelsius,
      celsiusToFahrenheit,
      add
  }