Final answer:
Mariah has 3 beads.
Step-by-step explanation:
To find the number of beads Mariah has, we can substitute the value of p, which represents the number of beads Aubrey has, into the equation p = 3q. Since Aubrey has 9 beads, we can write the equation as 9 = 3q. To solve for q, we divide both sides of the equation by 3, giving us q = 3.
Therefore, Mariah has 3 beads.