Hello!
The null hypothesis would be that the mean weight of tomatoes grown with the new fertilizer is not different to the mean weight of tomatoes grown with the new fertilizer (1,2 pounds)
The alternative hypothesis would be that the mean weight of tomatoes grown with the new fertilizer is larger than the mean weight of tomatoes grown with the new fertilizer (1,2 pounds).
This procedure is called a Statistical hypothesis testing. The Null hypothesis is the one that can't be rejected unless data shows that it is false, it usually involves a "no". The Alternative hypothesis is the one that you expect to prove. It usually involves saying that a given value is different, higher or lower than the one for the null hypothesis.
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