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Answer:
Measure of BC = 10.
Step-by-step explanation:
This is an isosceles triangle because the 2 base angles are both 50 degrees.
So the 2 sloping sides AB and BC are also equal.
JKM = M + L
15x - 48 = 40 + 5x + 12
10x - 48 = 52
10x = 100
x = 10
JKM = 15(10) - 48 = 102
180 = JKM + MKL
180 = 102 + MKL
MKL = 180 - 102 = 78