The two lines start at the same point outside the circle, using the intersecting Secants theorem, When you multiply the two dims for each line together, they are equal
For A:
5 * (5+x) = 6 * (6+4)
25 + 5x = 60
5x = 35
x = 35/5
x = 7
For B:
5 * (5+ 3) = 4 * ( 4+x)
40 = 16 + 4x
4x = 24
x = 24/4
x = 6
