Concept:
If \((h,k)\) is the midpoint of a segment joining a fixed point and a variable point, then the coordinates of the variable point can be expressed in terms of \(h\) and \(k\). Substituting into the given curve gives the locus of the midpoint.
Step 1: Let the midpoint of \(PQ\) be \(M(x,y)\).
Let
\[
Q=(X,Y).
\]
Since \(M(x,y)\) is the midpoint of \(PQ\),
\[
x=\frac{X+3}{2},
\qquad
y=\frac{Y+4}{2}.
\]
Therefore,
\[
X=2x-3,
\qquad
Y=2y-4.
\]
Step 2: Use the fact that \(Q\) lies on the circle.
Given
\[
X^2+Y^2=16.
\]
Substituting
\[
X=2x-3,
\qquad
Y=2y-4,
\]
we get
\[
(2x-3)^2+(2y-4)^2=16.
\]
Step 3: Expand and simplify.
\[
4x^2-12x+9+4y^2-16y+16=16.
\]
\[
4x^2+4y^2-12x-16y+9=0.
\]
Dividing throughout by \(4\),
\[
x^2+y^2-3x-4y+\frac94=0.
\]
Step 4: Write the final answer.
\[
\boxed{
x^2+y^2-3x-4y+\frac94=0
}
\]