Answer:
Step-by-step explanation:
The given length measures are the diagonals of the rhombus, so each side will be the hypotenuse of the triangle with legs half as long:
√(12² +10²) = √244 = 2√61 ≈ 15.62 . . . . side length
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The given angle measure is half the measure at ∠J. The full measure of ∠J is 100°, so the measure of ∠K is 180° -100° = 80°