SUMIF statement with two different conditions (Text based and checkbox) How can I create a SUMIF statement with multiple criteria?

I have a spreadsheets where I track hours for different clients in one table, and below this table I want to summarize in a summary table the hours per client if that work is finished and if it is billable.

My Statement would say, SUMIF:  


Textfield ClientName = "InsertClientName"  
Checkbox for billable hours = TRUE  
Checkbox for finished work = TRUE


So in my imagination it would have to be:
SUMIF(((ClientName="InsertClientName")&amp;(BillableHours=TRUE)&amp;(FinishedHours=True));Hours)

How can I create a formula like this?

I have browsed the Apple Help Forums and StackExchange, but they mostly show SUMIF Statements with one criteria, or people use IFAND Statements and every row to use that in their SUMIF Statement, but my problem is that I will at least need two criteria in my summary table All hours of ClientX where the hours are checked as billable.

Looking forward to your answers.
Just to make an official answer:

Use the SUMIFS() function to use 2 or more conditions.

From the documentation:


  The SUMIFS function returns the sum of the cells in a collection where
  the test values meet the given conditions.
  
  SUMIFS(sum-values, test-values, condition, test-values…, condition…)