Excel Function - NEED HELP

[Chapprr]

Trying to write a formula to calculate this:

$1 - 5000 30% $1500
5001 - 10000 24% 1200
10001-20000 20% 2000
20001 - 30000 16% 1600
30000+ 12% $$$$

Now I can get it to run my formula for anything above 30000, so it
calculates each "area" and then finds the difference between 30000 and
my number, then multiply's it by .12.

Here is my code for that

=IF(B14>30000,SUM((B14-30000)*0.12, SUM(E15+6300)))

But I cannot get it to work for anything below 30000!!! Here is my code
for it. It just keeps adding and I dont know how it is working or if
there is a better way

=IF(B18<5000,SUM(B18*0.3),IF(B18<10000,SUM((B18-5000)*0.24,SUM(E19+1500),
IF(B18<20000,SUM((B18-10000)*0.2,SUM(E19+2700))))))

Thank you sooooooooooooo much for your help.

Please send me an email if you have any suggestions.

Cheers