\frac{\partial{L(\hat{y}_{1, 1}, y_{1, 1}, \hat{y}_{2, 1}, y_{2, 1})}}{\partial{h^{1}_{i,j}}} = \frac{\partial{L(\hat{y}_{1, 1}, y_{1, 1}, \hat{y}_{2, 1}, y_{2, 1})}}{\partial{\hat{y}_{i,1}}} \frac{\partial{\hat{y}_{i,1}}}{\partial{h^{1}_{i,j}}}=(\hat{y_{i,1}}-y_{i,1})(w^{2}_{j,1})