4. In this partly completed pyramid, each rectangle is to be filled with the sum of the two numbers in the rectangles immediately below it.
What number should replace $x$ ?
A 3
B 4
C 5
D 7
E 12
4. A The calculations required to find the value of $x$ are:
$$
\begin{array}{l}
p=105-47=58 ; q=p-31=58-31=27 ; \\
r=47-q=47-27=20 ; \\
s=r-13=20-13=7 ; t=13-9=4 ; \\
x=s-t=7-4=3 .
\end{array}
$$
(Note that the problem may be solved without finding the values of four of the numbers in the pyramid. Finding these is left as an exercise for the reader.)