Not enough Input arguments (Adaptive RK method )

The photo attached is the question. Here is my script answer but error shows me that it has not enough input arguments in line 15. Can someone help me to fix this?

function[t,y]= P3(dydt,tspan,y0,h)
tspan=[0 4];
y0=0.5;
h=0.1;
ti=tspan(1);
tf=tspan(2);
t=(ti:h:tf)';
n=length(t);
if t(n)<tf;
    n=n+1;
end
y=y0*ones(n,1);
for i=1:n-1
    hh=t(i+1)-t(i);
    k1= feval(dydt,t(i),y(i));
    ymid=y(i)+k1*hh/2;
    k2=feval(dydt,t(i)+hh/2,ymid);
    y(i+1)=y(i)+k2*hh;
end
plot(t,y)
end

Not enough input arguments.

Error in P3 (line 15)
    k1= feval(dydt,t(i),y(i));

[Stephen23]

Duplicate:

https://www.mathworks.com/matlabcentral/answers/493736-error-showed-not-enough-input-arguments