A worker starts a new assembly process with the first unit taking $46$ minutes. $On$ the first day they produce $13$ parts. $On$ the second day, they produces $20$ parts. Furthermore, $it$ takes them $18$ min $to$ produce the $20th$ part $on$ the second day. Using the Crawford learning curve model, determine the learning rate. Enter the learning rate $as$ a percentage. Units are $"\%".$