What is the surface area of a triangular prism 6.5ft 8ft 6 ft 2.5 ft? 115square feet. 120 square feet. 135 square feet. 150 square feet.

I'd like to offer the alternative perspective. I think that learning grammar rules through a written account of the system (text books) is something that is only useful to a language learner under the following conditions:
they have already learned how to have a conversation in the language 
they are naturally curious now about how the patterns in how it fits together 
they would like to learn how to read in the language
they would like to improve their accuracy for a specific purpose (eg professional or educational)