For 1:
Use pythagorean theorem because of the radius tangent theorem(point of contact = 90 degrees)
12 is the hypotenuse (the right angle points at the hypotenuse)
Therefore:
(9)^2 + (x)^2 = (12)^2
81 + x^2 = 144
Subtract 81 from both sides of the equation
x^2 = 63
Square root both sides to get rid of square on x and isolate the variable
The square root of 63 = 7.93 (roughly)