3. Let the value of the six variables A, B, C, D, E, F are 5, 4, 2, 6, 3, 7 respectively. First, use a stack to transform the infix expression \( (\mathrm{A} + \mathrm{B})\mathrm{xC} - \mathrm{D} / \mathrm{E} + \mathrm{F} \) into a postfix expression. Then, use a stack to evaluate the obtained postfix expression. (15%)