Answer:
19: 106
20: 79
21: 70
Explanation:
Circle upper left
The central angles all add up to 360 degrees
BC + CD + 148 = 360
But CD = BC
2BC + 148 = 360 Subtract 148 from both sides
2BC = 360 - 148 Combine
2BC = 212 Divide by 2
BC = 106
20
3 of the 5 arcs are marked as being equal.
Let each of them be called = x
3x + 41 + 82 = 360 Combine
3x + 123 = 360 Subtract 123 from Both sides.
3x = 360 - 123
3x = 237
x = 237 / 3
x = 79
BC = 79
21
Unless DE and FC are diameters, this can't be solved. I will assume they are.
FB + 48 + 22 = 180.
FB + 70 = 180
FB = 110
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FC = FB + BD + DC
180 = 110 + 22 + DC
180 = 132 + DC
DC = 180 - 132
DC = 48
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BC = BD + DC
BC = 22 + 48
BC = 70