a) Adding to alpha position, so this must have come from the combination of an enolate and an electrophile.
b) Adding to the beta position, so this must have come from a Michael addition (also called a conjugate addition).
To carry out a Michael addition, the first step is to convert propanal to an alpha, beta unsaturated carbonyl.
To do this, perform an alpha bromination with (Br2/H3O+) and then do an E2 elimination (tBuOK/heat).
Then add a Gilman reagent to the alpha,beta unsaturated aldehyde to add a carbon-carbon bond at the beta position.
