One bad SAC score shouldn't drag down your AOS Mark or Study Score by too much, especially considering that it's not too far outside of your average mark.
Considering your high 80s average, and that 76% is just a bit off of that, I'd say you should be fine towards getting a 40 study score.
Economics can hold a competitive cohort, but your scoring does seem pretty robust. If you do just as well in the upcoming SAC and the exam, a 40 shouldn't be too hard.
When I did Drama (not sure if this is applicable, because the written SACs are marked differently to other subjects) I had a SAC average in the high 70s. My last SAC of the year was about 45% and I still got a B for that outcome. Sure, I wasn't aiming as high as you, but my score wasn't as badly affected as I thought it would be.
Whatever happens, you should continue trying your hardest in your subjects. You might be pleasantly surprised at the end of the year when you get your results, you know...