Step 1: Determine the order of the differential equation.
Given:
\[
\left(
\frac{d^my}{dx^m}+\frac{d^ny}{dx^n}
\right)^{p/q}
=
5\frac{d^ry}{dx^r}
\]
We are given
\[
n\lt r\lt m
\]
The highest order derivative present is
\[
\frac{d^my}{dx^m}
\]
Hence, order of the differential equation is
\[
m
\]
Given order is \(4\), therefore
\[
m=4
\]
Step 2: Find the degree of the differential equation.
To define degree, the equation must be free from fractional powers.
Raise both sides to the power \(q\):
\[
\left(
\frac{d^my}{dx^m}+\frac{d^ny}{dx^n}
\right)^p
=
5^q
\left(
\frac{d^ry}{dx^r}
\right)^q
\]
Now the highest order derivative is
\[
\frac{d^my}{dx^m}
\]
and its highest power is
\[
p
\]
Thus, degree of the differential equation is
\[
p
\]
Given degree is \(3\), hence
\[
p=3
\]
Step 3: Final conclusion.
Therefore,
\[
\boxed{m=4,\ p=3}
\]