Mother = 17 inches and then Newborn = 5 (2/3) or 5.66666666667 inches

I was sort of guessing based on your question what you were looking for. How I solved this is we know that since the average adult giraffe is 18 feet tall and the average newborn giraffe is 6 feet tall, then the adult giraffe is about 3 times as tall as the average newborn giraffe so the ratio is 3:1 adult: newborn. So with the mother at 17 inches, then since the newborn giraffe is, on average, 3 times smaller than the mother, it is therefore 17/3 = 5.666667 or 5 and 2/3s.