By the empirical rule, what percentage of the area under the normal curve lies to the left of mu, the average? put your answer as a percentage.

The normal curve is a bell shaped curve which is symmetric about μ (the population mean), as shown below.
When the curve is plotted against the normalized coordinate z, the curve is symmetric about z=0, which coincides with μ.

Because the total area under the curve is 1, each half of the curve about the line of symmetry has an area of 0.5.
Ths means that 50% of the normal curve lies to the left of μ.

50%