How to have conditional formatting into an if statement in excel?

In Excel how would you’ve a condition format that when another cell changes the format changes. Eg. My spreadsheet is for Conference room booking, and I enter what suite they would like, and they all have different numbers of people they have the ability to fit in them. How would you format it so it goes red when you have too many people that gets booked in, but that changes with the suite entered in.

Thanks for any help

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Answer:
if you have your suite name in column A, the number of people who can fit into the suite in column B and the number currently booked in in column C, then to perform a conditional format on rows B-C, do the following :

Highlight columns A-C

Choose Format->Conditional Formatting…

Select the condition “Formula is”

Type in the formula

=$C1>$B1

Add your formatting for cells that satisfy this criteria