A triangle has vertices P(−2, 5), Q(−2, −3), and R(4, −3). S is the midpoint of PQ and T is the midpoint of QR.

Plotting this on a piece of paper, and labeling all the points;

We have S midway of 8, which is 4

We have T midway of 6, which is 3

Thus, we have a right angle triangle, and we use this formula:

a^2+b^2=c^2

Plugging 4 for a, and 3 for b, we have

4^2+3^2=c^2

c^2=25

$c=\boxed{5}$

st=5, (a)