we know that
∡LKM=55°
if KM≡JM
then
∡JKM=45°
step 1
find KM
tan 55=12/KM------> KM=12/tan 55------> KM=8.40 cm
applying the Pythagorean theorem to the triangle KJM
JK²=KM²+JM²------> JK²=8.4²+8.4²----> JK²=141.12-----> JK=11.88 cm
the answer is
11.9 cm
