Two approaches to solving this one. In the first, more formal, approach, you need to remember the formula
for calculating the HALFWAVE dipole length in feet is 468/frequency in MHz. Before we plug and chug, though, we have to calculate what that frequency is, so we have to go back to the old standby frequency in MHz = 300/wavelength in meters. So:
3. Convert feet to inches. 9.36 feet * 12 inches/foot = about 112, which is the correct answer.
However, you really don't have to do all that much calculating since the possible answers are far apart from each other. Just remember that electricity doesn't move QUITE at the speed of light in a wire, so all we really have to do is take the halfwave length (6 meters/2)=3 meters, convert it to inches, and select the answer which isn't QUITE the number you calculated.
3 meters = 300 cm = (300/2.54) inches = 118 inches. Of the available choices, 112 fits the bill: 6 and 50 are way too short, and 236 is too long.