The two tangent theorem states that if we draw two lines from the same point which lies outside a circle, such that both lines are tangent to the circle, then their lengths are the same.
Which means that DB = CB
Which means that 10x + 16 = 5x + 20
10x - 5x = 20 - 16
5x = 4
x = 4/5
And so the length of CB is
5 * 4/5 + 20 = 4+20 = 24
Good LUCK :)
