mean = houses['SalePrice'].mean()
st_dev = houses['SalePrice'].std(ddof = 0)
houses['z_prices'] = houses['SalePrice'].apply(
    lambda x: ((x - mean) / st_dev)
    )

z_mean_price = houses['z_prices'].mean()
z_stdev_price = houses['z_prices'].std(ddof = 0)

mean_area = houses['Lot Area'].mean()
stdev_area = houses['Lot Area'].std(ddof = 0)
houses['z_area'] = houses['Lot Area'].apply(
    lambda x:((x-mean_area)/stdev_area)
    )

z_mean_area = houses['z_area'].mean()
z_stdev_area = houses['z_area'].std(ddof = 0)