Hi not sure if this counts as one question or not because the question just has multiple parts

Background The HP-35 was the first scientific hand-held calculator. released in 1972 and an immediate success with engineers and scientists. Amongst other features, it used an unusual of entering numbers, called RPN RPN (reverse Polish notation, n for Polish mathematician Jan amed Lukasiewicz) allows complex calculations to be entered without the use of parentheses. The key difference is that operators are entered after the operands, rather than between them The HP-35 implemented RPN using a stack of 4 registers, referred to as X, Y, Z, and T. The value in the X register is the one shown on the calculators LED display; the other registers are used for temporary values during calculations. New values are entered into the X register, with existing values "pushed" up the register stack: the old value of X goes into Y, the old value of Y goes into Z, the old value of Z goes into T, and the old value of T is lost. Single-operand functions (such as square root) use and replace the value in the X register, other registers are unchanged. Functions that operate on 2 values (such as the arithmetic operato rs) use the values in Y and X, with the result going back into X. Values in the Z and T registers are dropped" down the stack, with Z overwriting the old Y and T overwriting the old Z. The value of T is preserved, providing a simple way to do calculations with repeated values. This scheme allows calculations to be entered without using parentheses. For example, you could compute the compound expression (5 4Y(3-2) like this ENTER 4 3 ENTER 2