message: add duration
diff: @@ -20,6 +20,7 @@ export const rateOf = (cost: number, duration: Duration) => {
  switch (duration) {
  case Duration.P30D:
  return cost / 12;
  + case Duration.P7D:
  case Duration.P90D:
  case Duration.P3M:
  return cost / 4;
  