To find out how many collectible dolls Mariah can buy, we set up the equation based on the price of each doll and the total amount of money she has. Since each doll costs $4.50 and she has $75.00, we can represent the situation with the equation:
\[ 4.5d = 75 \]
Here, \( d \) represents the number of dolls Mariah can buy.
To find the number of dolls, we can solve this equation:
\[ d = \frac{75}{4.5} \]
Calculating that gives:
\[ d = 16.67 \]
Since she can't buy a fraction of a doll, we round down to 16. Therefore, Mariah can buy 16 collectible dolls.
The equation that represents this situation is:
4.5d = 75.