The basic theorem that's used here is,
' the angle at the centre of the circle is twice the angle at the circumference '.
So, in Q9, the angle at the centre TWV, will be twice the angle at the circumference TUV,
ie. angle TWV = 2 times 67 = 134.
It follows then, that 16x - 10 = 134,
16x = 144,
x = 144/16 = 9.
In Q10, angle KNM = 2 times (7x + 9) etc.
Q's 11 and 12 require a little more thought. Come back if you can't do them, (after you've tried to do them that is).