Answer:
x = 40
Explanation:
Given 2 secants to a circle from an external point, then
The product of the external part and the whole of one secant is equal to the product of the external part and the whole of the other secant, that is
8(8 + x) = 12(12 + 20) ← distribute parenthesis on both sides
64 + 8x = 12 × 32 = 384 ( subtract 64 from both sides )
8x = 320 ( divide both sides by 8 )
x = 40