Step 1: Identify the order of the differential equation
The given equation is:
\[
\frac{d^y}{dx^t} = c + \left( \frac{d^y}{dx^t} \right)^{\frac{3}{2}}.
\]
The order of a differential equation is the highest order derivative present in the equation. Here, the highest order derivative present is \( \frac{d^y}{dx^t} \), thus:
\[
\text{Order} = t.
\]
Step 2: Determine the degree of the equation
The degree of a differential equation is the exponent of the highest order derivative after it has been made polynomial in derivatives.
Here, the term \( \left( \frac{d^y}{dx^t} \right)^{\frac{3}{2}} \) has a fractional exponent. To make it a polynomial, we would need to raise everything to the power of \( \frac{2}{3} \), which results in:
\[
\text{Degree} = 2.
\]
Step 3: Compute the Sum
\[
\text{Order} + \text{Degree} = 4 + 2 = 6.
\]
Step 4: Final Answer
Thus, the sum of the order and degree of the given differential equation is:
\[
\boxed{6}.
\]