When lucentio's real father arrives and discovers the teacher posing as him and Tranio in his sons clothes, Lucentio is forced to confess to the whole plan. He tells them about his new marriage to Bianca.
Baptista is telling Bianca that she isn't allowed to marry until her sister Katherina does
so yeah, 2+2=4
Lucentio disguised himself as a latin tutor to get closer to Bianca
Petruchio devises a scheme to prove whose wife is the most obedient. Bianca and the widow fail to come to their husbands when called. But Katherine returns