3(10 - x) = 21
30 -
21
30 - 3x
= 21
- 3x
- 3x
-9
=
X =

Step-by-step explanation:

I am answering blanks left to right and top to bottom.

3x

30 30

-9

-3 -3

x = 3

∠acb = 8°

step-by-step explanation:

∠xba lies on the circle and is half the measure of the intercepted arc ax

hence

measure of arc ax = 2 × 42° = 84°

∠acb is outside the circle and is

∠acb = (arcab - arcax ), hence

∠acb = 0.5 (100 - 84) = 0.5 × 16° = 8°