In order to combine everything into one equation, you need to figure out how many moles of sugar you're adding. Brown sugar is a homogeneous mixture of various compounds, but we'll just make an assumption that it has the same molecular weight as table sugar does (C12H22O11, 342 g/mole). Looking online, I found the density of brown sugar to be about 0.721 g/mL. So your half-cup has 85.29006 grams of sugar. For the Freezing Point Depression equation, we'll combine the moles of sugar with twice the moles of salt to come up with the overall molarity of the solute. (We'll use twice the moles of salt since NaCl dissociates into two ions, and then use 1 for the van't Hoff Factor).
Delta Tf = Tf0 - Tf= i Kf m
Tf0 = 0C
i = 1
Kf = -1.86C/m
m=(molesNaClx2 + molesC12H22O11)/7.29L = 0.572589M/L solute.
Tf -0 = (1)(-1.86)(0.572589) = -1.06502 C
Tf = 30.083 Degrees Fahrenheit.
As you can see, the large amount of liquid you have in there causes the dilution factor to be VERY large so you're not going to see a huge depression in the freezing point. In reality, you can assume that it will freeze at the normal freezing point of water.