A reverse polish notation (RPN) calculator uses a stack. The calculator works as follows: Entering a number puts it on top of the stack and entering an operation op causes the topmost number x and second topmost number y to be popped off the stack and the number y op x to be pushed on the stack. Thus an operation zopy is entered as ryop. For example 1 +2 is computed with "1 2 +" and (2 * 3)-4 is computed with "2 3 * 4- How do you calculate the following expressions with a RPN calculator?

a) 1+3+5-7

d) (3+4) (20 (3* 4+2))

c) 3 (2+4 3)