To determine how long it will take for the water tank to be emptied, we would need to analyze the graph in question. Since I cannot see the image, I can't provide a specific answer directly from it.
However, if the graph shows a declining line representing the water level over time, look for the point where the line intersects the horizontal axis (the x-axis), which would indicate the time at which the water level reaches zero.
If the options provided are 35 hours, -3 hours, 11.7 hours, and 12 hours, you should select the option that corresponds to the time axis intercept where the water level is zero.
Please review the graph and choose the option that matches that intercept. Typically, the correct answer is likely to be a positive value representing hours. If, for example, the line intersects the x-axis around the 12-hour mark, then "12 hours" would be the correct response.