Hypothesis Tests · Superchallenge problem

A taster is given $8$ cups of tea, told that exactly $4$ had milk poured first, and must pick those $4$. She picks $3$ of the $4$ correctly. Under $H_0$ (she is guessing, so every choice of $4$ cups is equally likely), find the $p$-value $P(\text{at least } 3 \text{ correct})$.