float totalSizeX = 300f;
int nbSlotX = 4;

float slotSizeX = totalSizeX / nbSlotX;
float center = totalSizeX / 2f;

float slot1Start = -center;
Vector2 slot1SurfaceX = new Vector2(slot1Start ,slot1Start + slotSizeX);

float slot1EndSurface = slot1Start + slotSizeX;
Vector2 slot2SurfaceX = new Vector2(slot1EndSurface, sslot1EndSurface + slotSizeX);