FWIW, I took my ASTB without studying and with only about 20 hours under my belt, and passed. I then re-took the ASTB after studying the ARCO for a bit and got a better score. However, I felt that my weakness' were in the first half of the test, rather than the last, and therefore I studied up on my math a bit, so I'm sure that was a contributing factor as well. YMMV. But I'm sure since you have an engineering degree that your math skills are exceptional.