In the diagram below, PQR is a triangle, right-angled at Q. A point S

(1) We could calculate the area of PQR. However, we can't calculate the area of SAQB. Insufficient.

(2) Since SAQB is a square, we could calculate the length of SA=SB based on the length of QP and QR.

We have \(S_{PQR}=\frac{1}{2} * PQ * QR\)

We also have \(S_{PQR} = S_{PQS} + S_{SQR}\\
= \frac{1}{2}*PQ * SA + \frac{1}{2} * QR * SB \\
= \frac{1}{2} * SA * (PQ + QR)\)

Hence \(\frac{1}{2} * PQ * QR = \frac{1}{2} * SA * (PQ + QR) \implies SA = \frac{PQ * QR}{PQ + QR}\)

However, we can't know the length of PQ and QR. Hence insufficient.

Combine (1) and (2):
From (1) we could calculate the area of PQR
From (2) we could calculate SA=SB so we could calculate the area of SAQB.

Hence, we could calculate "the area of SAQB as a fraction of the area of triangle PQR". Sufficient.

The answer is C.