One projected at \alpha from the horizontal and other from the vertical.
For the stone \alpha from the horizontal
x = 30*4/5
x = 24
Y = 30*3/5 - 10/2
Y = 18 - 5
Y = 13
For the stone \alpha from the vertival
X = 30*3/5
X = 18
Y = 30*4/5 - 10/2
Y = 24-5
Y = 19
D1 =√ (576 + 169) = 27.3
D2 = √(324 + 361) = 26
Distance between them = 6√2