Even though this is a grid-in question, we can actually plug-in to solve. That's because they don't ask us for the areas themselves, they ask us for the RATIO of the areas.
Say QS = 1, QV = 3, PT = 3, and PR = 4. That's going to mean that SV = 2, since it's the difference between QV and QS.
Our areas:
▵PST = ½(SV)(PT) = ½(2)(3) = 3
▵PQR = ½(QV)(PR) = ½(3)(4) = 6
So the ratio of ▵PST to ▵PQR = 3/6, or 1/2. You could also grid in .5.