Hypothesis testing — practice question

Earlier, the yearly quantity of wheat produced per farm by a large number of similarly sized farms in one region had a mean of $24.0$ tonnes and a standard deviation of $5.2$ tonnes. Last summer a new fertiliser was applied on all the farms, and it was expected that the mean quantity of wheat produced per farm would exceed $24.0$ tonnes. To check whether this was correct, a scientist recorded the amounts of wheat produced by a random sample of $50$ farms last summer. He found that the sample mean was $25.8$ tonnes.