Tonne or Ton (tonelada)
A tonne is 1000kg, whereas a ton is ≈907kg (2000lbs). Spanish people refer to 1000kg, and therefore a tonne. (I don't know about Spanish speaking s.americans).
So when I answer tonne am I correct or is Duolingo correct to tell me it is ton.
In Spanish speaking countries a ton is almost never used. When we say "tonelada" we almost always mean tonne. However both ton and tonne are translated as tonelada, since we already know that in the US people don't commonly use the metric system. So when we need to make a distinction we normally say "tonelada métrica" for tonne and "tonelada inglesa" for ton.
For the purposes of the sentences, they should both be correct. As gsrdzl pointed out, in Spanish, the difference in the type of "tonelada" is marked by adjectives like "métrica/inglesa/corta/larga".