Need help in creating a sliding scale commission worksheet

Thanks in advance for any help you can provide. I am trying to figure out how to best create an Excel worksheet that calculates real estate commission splits as they are received over the course of a calendar year. Like many real estate offices, agents have thresholds which reward them with better splits as their production continues to grow. The worksheet would catalogue commissions as they are received and calculate the splits as they pass each threshold.

From $0.00 - $75,000 70% of gross commissions rec'd
from $75,000 - $150,000 75% of gross commissions rec'd
$150,000 + 80% of gross commissions rec'd

I have tried a number of nested if functions, but one commission could can take you from say $70,000 to $155,000 which creates too many scenarios to test for. I've uploaded a stripped down worksheet which hopefully shows you what I'm talking about.

I appreciate your help!