In this question, we need to determine how many sixty watt (60 W) bulbs can be safely used in a 240V supply with a 4-ampere fuse. To do this, we need to consider the power and current rating of the bulbs and the fuse.

The power rating of each bulb is 60 W, and the supply voltage is 240 V. Using the formula P = IV (power = current x voltage), we can calculate the current required for each bulb: 60 = I x 240. Solving for I, we find that the current drawn by each bulb is 0.25 amperes.

Now, let`s consider the fuse. The fuse has a rating of 4 amperes, which means it can safely handle up to 4 amperes of current. Since each bulb draws 0.25 amperes, we can calculate the maximum number of bulbs that can be safely used by dividing the fuse rating by the current drawn by each bulb: 4 / 0.25 = 16 bulbs.

Therefore, the correct answer is option 4: 16. We can safely use 16 sixty watt bulbs in the given setup.