Lets say we have
$h[n] = ((1/2)^n )(u[n])$
now if we are ask, find h[k-n], then isn't it we should just swapped every 'n' with 'k-n'. So it turns out
$h[k-n] = ((1/2)^{k-n})(u[k-n])$
But why here in letter b
h[n] there is $((1/2)^n)(u[n])$ and if we find h[m], we simply change every 'n' with m so it yiels
$h[m] = ((1/2)^m)(u[m])$
now, if we find h[n-m], it should become
$h[n-m] = ((1/2)^{n-m})(u[n-m])$
but h[n-m] according here in solution manual 
is
$h[n-m] = ((1/2)^m)(u[n-m])$.
Why is that the exponent of '1/2' is only 'm', not 'n-m'?