Instead of recalling the count directly, it helps to look at the citation the Nobel committee gave for the 2018 Economic Sciences prize, since that explains how many distinct contributions were being honoured.
The 2018 prize recognised two separate strands of work in long-term macroeconomic analysis: one for integrating climate change into growth models, and another for integrating technological innovation into growth models. Because these were credited to two different economists working independently on their respective strands, William Nordhaus for climate-linked growth analysis and Paul Romer for innovation-driven growth analysis, the prize was split between exactly two people.
the correct answer is 2.