First, you need to know the rule.
When you have two secants drawn to a circle from an outside point, each secant is cut in two segments as it intersects the circle. In your first problem you have one secant with segments of lengths 5 and x. The other secant has segments of leng4ths 4 and 6.
The first secant has total length 5 + x.
The external segment is 5.
The second secant has total length 6 + 4.
The external segment is 6.
Rule:
If two secants are drawn to a circle from an outside point, then the product of the length of a secant and the length of its external segment equals the product of the length of the other secant and the length of its external segment.
First problem:
5(x + 5) = 6(6 + 4)
5x + 25 = 60
5x = 35
x = 7
Second problem:
4(x + 4) = 3(3 + 5)
4x + 16 = 24
4x = 8
x = 2