Since each girl donated 1 ½ feet of hair, we can add their donations together to get the total amount of hair donated:
1 ½ feet = 18 inches (since 1 foot = 12 inches)
So, each girl donated 18 inches of hair, and the total amount of hair donated by all three girls is:
18 inches + 18 inches + 18 inches = 54 inches
Therefore, all three girls donated a total of 54 inches of hair.