we know that FG=GH=HJ=JK or in other words, all small labeled segments are equal and there are 4 of them enclosed, so since the whole thing is 16.8 long, we can just divide it by 4 to get the length of any of them, so 16.8 ÷ 4 = 4.2, so FG = 4.2 and since HK is using up two enclosed segments that's twice 4.2 or HK = 8.4.