One way:
LaminaSress = zeros(3, NumLayers); %assuming that the result of your equation is a 3 elements vector
for layer = 1:NumLayers
LaminaSress(:, layer) = Qs*(Strain+z(layer)*Curve);
end
xlswrite(Filename, LaminaStress, 1, 'B32');
Note that assuming that z is a vector and Qs or Strain and Curve are also vectors , your loop is not even needed. You can get the whole matrix in one go:
LaminaSress = Qs.*(Strain + z .* Curve); %some tranposition may be needed to make sure the vectors are along different dimensions
xlswrite(Filename, LaminaStress, 1, 'B32');
