So in this question, you're looking at the upper tail not the lower tail so you would use the upper values (you're trying to find evidence that the new fertiliser would improve the number that survive.
if you were finding the lower tail(evidence to say the new fertiliser would reduce the numbers), you would use the lower values which is what you did but that's not what the question is asking.
Therefore, you are trying to test whether the value is greater than 12 which is what would show that the numbers did in fact improve so we use upper values since it would realistically give us values around what we should be expecting and if not we reject the alternative hypothesis.
test around the 10% SL and use your calculator to find values around 0.9, subtract from one and see if they are above or below the SL
P(X≥17)=1-P(X≤16)=1-0.9416=0.0584 < 10%
So your critical region would be values greater than or equal to 17 ( we can reject Ho)
HOPE THAT MAKES SENSE!