Answer
The number in the descended box is $~~42$
Work Step by Step
The number of protons must be conserved in the process.
$^{235}U$ has 92 protons
$^{132}Sn$ has 50 protons.
We can find the number $N$ in the descended box:
$92 = 50+N$
$N = 42$
The number in the descended box is $~~42$
