Hi guest, think of the question as 4 parts.

First part is heads. The probability of that occurance is 1/2 because it is either heads or tails.

Second part is tails. The probability of that occurance is also 1/2 because it is either heads or tails.

Third part is heads. The probability is 1/2 same reasoning of the First and Second part

Fourth part is tails. The probability is 1/2 same reasoning.

Multiply them together, \(\frac{1}{2}*\frac{1}{2}*\frac{1}{2}*\frac{1}{2}=\frac{1}{2^4}=\boxed{\frac{1}{16}}\)

Your welcome, Evan