Explanation:
Lucia is right. Faye is wrong.
because
3y³(7 - 3y) = +21y³ - 9y⁴
that is different to
-21y³ - 9y⁴
they have to remember : the outward sign (and factor in general) then applies to all terms inside the brackets when doing the multiplication.
so, if we need only negative terms as result, we need either a negative outward sign and all inward signs are positive, or we have a positive outward sign, and all inward signs must be negative.
mixing things up will not work for this goal.