The focal point of a mirror is half of the radius of curvature. We can use the formula, 1/f = 1/v + 1/u where f is the focal length , v is the image distance and u is object distance The distance of the star is assumed to be incredibly far away and 1 divided by a really big number is approximately zero, thus; 1/f = 1/v = 1/75 = 1/v therefore; the image is formed 75 cm infront of the mirror