number of people in front of James --- x
number of people behind James ----- x+1
entire line = james + in front + behind
= 1 + x + x+1
= 2x+2
2x+2 = 2(x+1)
0=0 ----> true for all x's
There is an infinite number of solutions,
just plug in any value of x
e.g.
x = 20
number in front of him = 20
number behind him = 21
total = 1+20+21 = 42
x = 45
total = 92
Since the total is 2x+2, and 2x+2 is always an even number,
any even number for the total will work
e.g. total = 246
in front = 122
behind = 123
James = 1
total = 246
All of the given choices are possible, however, if the trick part is to eliminate those that would not "reach down the block", we get into a different argument.
Certainly 100 could reach down the block, but probably 10 wouldn't.