I'm having trouble finding the value of "a" on question #3 on one of the attached "Calculus 1 Final Exam Review (=Practice Exam) (Questions).pdf" file.

I found b = 1 but I don't know how to find a.

My work is attached as the "mywork.pdf" file and the specific work for this problem is on page 10/11 of that pdf file.

Any help would be greatly appreciated!

Thanks in advance!