Aida applied the distributive property to write the equivalent expressions below. 15 + 21 = 3 (4 + 8)

What is Aida’s error?
Aida used 3 as the factor, which is not common to 15 and 21.
Aida did not correctly divide by the common factor to get (4 + 8).
Aida did not apply the correct operations to the expressions.
Aida wrote two expressions that are not equivalent.