Translation:I take the bus to go to grandma's.
I used granny rather than grandma and it was marked wrong However granny is quite common in English. Some people also say nanny or nanna - I suppose they would also be considered incorrect. It is really quite annoying for a native English speaker to have their English marked as wrong; we are trying to learn ITALIAN
This is a very awkward sentence in English. Most people would say something more like "I take the bus to go to my grandmother's house". It is unusual to leave out a qualifier like 'my' to denote which grandmother. It is also generally considered incorrect to have a possessive adjective like "grandma's" without an object (e.g. 'house'). Otherwise it is unclear to the reader where you are going - her house? her farm? her grave?