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Explanation:
Apply the law of cosines
j^2 = k^2 + l^2 - 2kl*cos(J)
(4)^2 = (6)^2+(2.8)^2 - 2*6*2.8*cos(J)
16 = 36 + 7.84 - 33.6*cos(J)
16-36-7.84 = -33.6*cos(J)
-27.84 = -33.6cos(J)
-33.6cos(J) = -27.84
cos(J) = (-27.84)/(-33.6)
cos(J) = 0.828 5714
J = arccos(0.8285714)
J = 34.0477353
J = 34 degrees approximately
Side note: Unfortunately lowercase L's look identical to the number one.
