If S means '-', Q means 'x' , R means '÷' and P means '+' then 1 P 45 R 2 Q 2 S 4 =?

After replacing the sign according to question
1   P   45   R   2   Q   2   S   4
Apply the BODMAS Rule
= 1 + 45 ÷ 2 x 2 - 4
= 1 + 22.5 x 2 - 4
= 1 + 45 - 4 = 42