Write out a truth table of the five bits for all positive numeric values > zero. Use Combinatorial logic (sum-of-products) to create a single output which is true for 9<=value<=15.
I think you probably mean (or the author probably meant) "diminished radix complement" for DC. Break it down into pieces. What does the msb tell you in either case? Assuming that the number in question is positive, how can you use just the lower four bits to determine if the value is greater than 9? What would be the result if you subtract 9 from the number?