float totalSize = 300;
int nbSlot = 3;

var slotSize = totalSize / nbSlot; //100

Vector2 slot1 = new Vector2(0,slotSize);
Vector2 slot2 = new Vector2(slot1.x + (solotSize /2), slot1.x + (solotSize /2) + slotSize);
Vector2 slot3 = new Vector2(slot2.x + (solotSize /2), slot1.x + (solotSize /2) + slotSize);