$15-18$ Kate Drew has been hand$-$painting wooden Christmas ornaments for several years. Recently, she has hired some friends to help her increase the volume of her business. In checking the quality of the work, she notices that some slight blemishes occasionally are apparent. A sample of $20$ pieces of work resulted in the following number of blemishes on each piece: $0,2,1,0,0,3,2,0,4,1,2,0,0,1,2,1,0,0,0,1.$ Develop upper and lower control limits for the number of blemishes on each piece.