What is √36ab^4c^5?

You'll need to use parentheses to indicate what is under the first radical sign and what is not. Did you mean radical (36a) or just radical 36?

I will assume that you meant radical (36a).

Then you have [radical (36a} * (b^4) * c^5.

This comes out to 6sqrt (a) * b^4*c^5.