The student is incorrect because if they were to reflect point A over the X-axis, this would mean they are moving it from its current quadrant to the one below. In that quadrant, the Y coordinate will be negative. So it couldn't possibly (6,3), because the 3 isn't negative.
Answer:
AR is 3 using Pythagoras 5^2 - 4^2 = 3^2. sin R is just sin (AC/RC). cos is adjacent over hypoteneus. tan is oppositve over adjacent. and sec is 1/cos, csc is 1/sin, and cot is 1/tan.