If you sketch the triangle, you need to understand that 12 is the length of opposite side (opposite to theta). Then the longest side is 13 is the hypotenuse. The other side with length 5 is the adjacent side. Thus from the definition of sin(theta)=opposite side/hypotenuse=12/13. A question for you, what is cos(theta)? cos(theta)=5/15 and tan(theta)=12/5
The labeled angle is what's called an inscribed angle. There's a theorem (fittingly called the inscribed angle theorem) that says the measure of this angle is half the measure of the circular arc that it subtends.
In this case, the angle is subtended by an arc measuring 180°. So
(4x + 6)° = 1/2 • 180°
4x + 6 = 90
4x = 84
x = 21
The answer is B)
~kashout
