If 75% of Brannan's class attended her twelfth birthday party, we can find the number of students who came to the party by multiplying the total number of students in the class by the percentage that attended.
First, we need to convert 75% to a decimal by dividing by 100:
75% = 75/100 = 0.75
Next, we can multiply the total number of students in the class by the decimal that represents the percentage who attended:
Number of students who came to the party = 0.75 * 24
Number of students who came to the party = 18
Therefore, 18 students came to Brannan's twelfth birthday party.