I think this may well be one of the cases where it's kinda counterintuitive that / doesn't do what you think it does.
the '/' operator (mrdivide) is not identical to the './' operator (rdivide). I believe what you're looking for is the element-wise division (rdivide) and that your code should be
nl = [1 , 2];
ns = [2 , 3];
payload = [300 , 400];
x = 1*nl;
y = 0.4*ns;
bonus = [0.5 + (1 *nl) + (0.4 * ns)];
T = [ 5 , 8];
d = payload .* bonus;
e = sqrt(d);
f = 80 * e;
fs = f./T;
plot(fs,payload)
