I learn and teach English and I have a question about `formal subject` and `formal object`
In this sentence from my grammar exercise book below,
`How much will it cost to repair the house?`
My friend and I thought `it` in the sentence is formal subject, but my grammar book says `it` is formal object. Which is correct? and Why?
for context, earlier tonight i had a stupid idea to light a small fire in a small kitchen pot and set it on the toilet lid, and cook hot dogs over it. i know that was dumb i have no self control but thats not my issue right now. does anyone know how to get this mark off