In order to calculate the cost of 1/2 pound of tea, let's first convert the mass from pound to kilogram.
Since 1 pound is equal to 0.45 kilogram, 1/2 pound is equal to 0.225 kilogram.
Then, since 1 kilogram of tea costs $15.99, 0.225 kilogram of tea costs 15.99 * 0.225 = 3.6.
Therefore the cost will be $3.60.