Conditional Formatting - How to use formula type???

Every month I have to manually modify this table (which is time-consuming).

If "RVUs YTD" is greater than the "RVU target", I want a green checkmark and if its less then I want a red X. I have already achieved this as you can see in my screen shot, but, I have to modify these each month manually (these values increase each month) .

In my second screen shot, if I select "type" and make it "formula", how can I achieve to do this automatically?

What do I type in the value box so that if B4>D4 it will make it green automatically?

Thank you

*I have attached the spread sheet.

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