If two secants intersect from a point outside of the circle, then the product of the lengths of the secant and its external segment equals the product of the other secant and its external segment.
#1
5(x+5) = 6(4+6)
5x + 25 = 6 * 10
5x = 60 - 25
5x = 35
x = 7
#2
4(x+4) = 3(5+3)
4x + 16 = 3 * 8
4x = 24 - 16
4x = 8
x = 8/4
x = 2