Answer
C(4,$\frac{-5}{2}$)
Work Step by Step
Points A and B have symmetry with respect to point C.
To find the coordinates of C given the points:
A(3,-4) and B(5,-1)
C is the mid point of A and B
M=($\frac{x1+x2}{2}$, $\frac{y1+y2}{2}$)
C = ($\frac{3+5}{2}$, $\frac{-4-1}{2}$)
C(4,$\frac{-5}{2}$)
Therefore the coordinates of B(4-a,6-b)