The postfix expression will be,
A B C D + * F / + D E * +

→ '10' is pushed in the stack

→ '5' is pushed in the stack

→ '+' comes so addition will be done by popping the top two elements in the stackand the result is pushed back into the stack, i.e., 10+5 = 15

→ 60 pushed in the stack

→ 6 pushed in the stack

→ '/' comes. So, 60/6 = 10

→ '*' comes. So, 15 * 10 = 150

→ '8' comes, push in the stack

→ '-' comes. So, 150-8 = 142

So the final result is 142.

a / b - c + d * e - a * c
* Start scanning the expression from RHS. * Push the operators on the top of the stack by ensuring that only high priority operator can be pushed over a low priority operator.
* If a low priority operator is encountered in expression while scanning it, and if top of stack have high priority operator then pop it and after that push low priority operator on top of stack.
* Print each operand just after scanning it.

The given infix expression is,
(A + B + (C + D))/ (F + D + F)
⇒ Push ‘(’

⇒ Read A

⇒ Push ‘+’

⇒ Read B

⇒ Since ‘+’ is Left associative, so ‘+’ in stack will have higher procedure then the current ‘+’, hence pop it,

⇒ Push ‘+’

⇒ Push ‘(’

⇒ Read C

⇒ Push ‘+’

⇒ Read D,

⇒ Now on looking ‘)’ we will pop all the operators till first ‘(‘,

⇒ Pop

⇒ Push /

⇒ Push ‘(’

⇒ Read F,

⇒ Push ‘+’

⇒ Read D,

⇒ Since + is left associative, so pop ‘+’,

⇒ Push up

⇒ Read E,

⇒ Since ‘(’ came so pop till ‘)’,

⇒ Pop ‘/’

Hence, postfix expression is,
AB + CD ++ FD ++ E +/

Prefix: -*+ABC*-DE+FG
Read the Prefix expression in reverse order (from right to left)
GF+ED-*CBA+*-
If the symbol is an operand, then push it onto the Stack
If the symbol is an operator, then pop two operands from the Stack
Create a string by concatenating the two operands and the operator between them.
string = (operand1 + operator + operand2)
And push the resultant string back to Stack

=>
C*(A+B)-(D-E)*(F+G)
which is equivalent to =>
(A+B)*C-(D-E)*(F+G)