6. Some of the digits in the following correct addition have been replaced by the letters $P, Q, R$ and $S$, as shown.
What is the value of $P+Q+R+S$ ?
A 14
B 15
C 16
D 17
E 24
\begin{tabular}{r}
$P 45$ \\
$+\quad Q R \quad S$ \\
\hline 654
\end{tabular}
6. B From the Units digit we see that $5+S$ ends in a 4 , so $S=9$ (and 1 is carried). Then the Tens digit has $4+R+1=5$ so $R=0$ (and nothing carried). Finally, the Hundreds digit gives $P+Q=6$. Then $P+Q+R+S=6+0+9=15$.