Exactly what are you trying to calculate?  Using the values you've given,
tell us what you intend to do with them and what your expected result is,
please.

But maybe something like this:
A1 = 4.95%
A2 = 3500
A3 = 43500
A4 = user entered value (as 45000)
formula could be
=IF(A4-A2>A3,"Too Much",IF(A4<=A2,0,(A4-A2)*A1))
which says
if the amount after subtracting 3500 from the user entered value is greater
than the limit set in A3 (43500) then say "Too Much", but if that is ok, then
if the user entered value is below the exempt value, then show zero,
otherwise, take the user entered amount, subtract the exempt amount from it
and multiply that by the percentage in A1 and show the result: 2054.25 in my
example using 45000 as the user entered value.