Answer: 1/4
Step-by-step explanation:
You flipped the coin 4 times and got only one tail in those four flips. So that's where the 1/4 comes from when you state the experimental probability of tails is 1/4.
The theoretical probability of tails is 1/2 assuming it's a fair coin, as each side is likely to land on. The theoretical probability is one that can be calculated without having to do the experimental trials.
Subtract the two fractions: 1/2 - 1/4 = 2/4 - 1/4 = (2-1)/4 = 1/4