A "crossed aldol addition" uses two different aldehydes or ketones. One of these compounds has alpha protons and can therefore be enolized, so it becomes the nucleophile. The other compound has no alpha protons and thus cannot be enolized, so it must serve as the electrophile.
In this problem, you'll first draw the mechanism of the crossed aldol addition between propanal and benzaldehyde. In Part 2, you'll show the aldol addition product that forms when the enolizable carbonyl compound from Part 1 (propanal) reacts with itself.

Part 1: When drawing the requested mechanism, don't forget to include all lone pair electrons and non-zero formal charges, and don't include byproducts unless they are requested.
Box 1: Draw curved arrows to enolize one of these compounds with hydroxide ion. You will have to draw in a hydrogen atom.
Box 2: Draw the enolate from the first step and use curved arrows to show how it reacts with the electrophile.
Box 3: Draw the intermediate resulting from the previous step and use curved arrows to show its reaction with water.
Box 4: Draw the final organic product of the reaction, including lone pair electrons.

Part 2: Draw the structure of the self-aldol addition product that would form from propanal. Don't forget to include lone pair electrons!