A TV tower stands vertically on a bank of a canal. From a point on the other bank directly opposite the tower. the angle of elevation of the top of the tower is 60º. From another point 20 m away from this point on the line joining this point to the foot of the tower, the angle of elevation of the top of the tower is 30º (Fig. 11.42). Find the height of the torwer and the width of the canal.