How can i use doubles when multiplying with 4 to find 4/8?

Greg is designing a clock face. using the center of the clock as the origin, he keeps its diameters at 10 units. match the positions for the hours on the clock face to their corresponding coordinates. 3 o'clock (0,-5) 6 o'clock (5,0) 9 o'clock (0,5) 12 o'clock (-5,0)