The missing sides in the figure are
HJ = 2.14
KJ = 6.43
How to find the missing sides
Examining the figure, the pair of equivalent sides are
HI and KL, IJ and JK, then HJ and JL
The solution is worked out using the proportions as follows
KL / HI = KJ / JI
9 / 21 = KJ / 15
KJ = 15 * 9/21
KJ = 6.43
Solving for HJ
KL / HI = HJ / JL
9 / 21 = HJ / 5
HJ = 2.14