1) if to substitute the given coordinates and slope into the common form of equation (it is y=s*x+i), then 0=3*1+i, ⇒ i= -3. The required equation is y=x-3.
C. y=x-3.
2) according to the condition coordinates of R are (x;0). Then it is possible to calculate the x-coordinate of R after substitution into the slope-interception form (it is y=s*x+i): 0=2x-8; ⇒ x=4. The coordinates of R are (4;0).
A. (4;0).