<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def ResidualFeedForward(feature_depth, feedforward_depth, dropout, mode):
 """Residual feed-forward layer with normalization at start."""

  return layers.Residual(
      layers.LayerNorm(),
      layers.Dense(feedforward_depth),
      layers.Relu(),
      layers.Dropout(rate=dropout, mode=mode),
      layers.Dense(feature_depth),
      layers.Dropout(rate=dropout, mode=mode)
  )