You can't calculate the product of a number and a function handle. What you can do instead is calculate the product of a number and the result of evaluating that function handle.
fh = @(x) x.^2;
This works and returns a number. It evaluates the function handle with x = 5 then multiplies that result by 2.
y1 = 2*fh(5)
This works and returns another function handle that you can evaluate. Note that inside the function handle fh2 I evaluate fh at the value that was passed into fh2.
fh2 = @(x) 2*fh(x)
y2 = fh2(7) % Essentially the same as y1 (except with x = 7 instead of x = 5.)
This does not work which is why I put it last.
y3 = 2*fh
