let Tom has y dollars and Anita' has z dollars.
we have to equations:
y = x + 2*z
x-1 = 2*(z-1)
So, y = x + (x-1) +2 = 2*x + 1
what is confusing here, at least for me, is "If Paul and Anita cost one dollar"
once walker explained that this means minus one, the rest is simple algebra.
this is the way GMAT works. they mess with your head:)