Answer: Positive.
Step-by-step explanation:
Suppose there are two related goods, i.e, Good A and Good B.
Cross price elasticity of demand refers to the responsiveness of demand for Good A if there is a change in the price of its related good, i.e, Good B.
Now, we are talking about gasoline and public transportation, suppose if there is increase in the price of gasoline then it will be costlier for the people to drive their own cars, as a result demand for public transportation increases.
There is a positive relationship between the gasoline and public transportation.
Hence, cross-price elasticity of demand between gasoline and public transportation is Positive.