The steps are as follows:
$d/(e+f)+b*c$
$\implies ((d/(e+f))+(b*c))$
$\implies((d/ \ ef+))+(b*c))$
$\implies ((def+/)+(b*c))$
$\implies (def+/)+\ bc*$
$\implies def+/ \ bc* \ +$
Option $(C)$ is correct.
Note :1) Parenthesis $()$ is having the highest priority and associativity is left to right.
2) Division $(/)$, multiplication $(*)$ having less priority than parenthesis but high than addition $(+)$ operator. all of them having associativity is left to right.
3) In infix expression operator is placed between operand while in postfix expression operator followed their operand.