You have to plug in -6 into the variable n
so it would look like this:
f(-6) = -6^4+5(-6)^3 -(-6)^2+33(-6)+15
then you can use a calculator and solve it (don’t forget to use PEMDAS)
f(-6) = -1296+ 5(-216) - 36+ (-198) +15
f(-6) = -1296-1080-36-198+15
f(-6) = -2595
I hope this helps you understand it better!