25. Let \( a, b, c \) be three distinct real numbers, none equal to one. If the vectors \( a \hat{i}+\hat{j}+\hat{k}, \hat{i}+b \hat{j}+\hat{k} \) and \( \hat{i}+\hat{j}+c \hat{k} \) are coplanar, then \( \frac{1}{1-a}+\frac{1}{1-b}+\frac{1}{1-c} \) is equal to