c3 graph questionnnnn

Given that f (x) = a| x – b| – 1, where a and b are constants,
(c) state the value of a and the value of b.

heyyy guys, so this is a question im a bit stuck on how to work out. ive had a look at the mark scheme where it says the answer`s
One of a = 2 or b = 6

a = 2 and b = 6

i dont understand how they came to this answer :/
(ps this is for c3 tomorrow so any help today will be greatly appreciated thank you!)

this is the full paper and it`s question 4
- theres a bit preceding it which may or may not be related to how they got the answer, i dont know

https://qualifications.pearson.com/content/dam/pdf/A%20Level/Mathematics/2013/Exam%20materials/Question-paper-Unit-C3-(6665)-June-2014.pdf

bumpty bump

there probably is an easier way to do it but, you have 2 unknowns with 2 coordinates which will help you to form 2 equations.

such as :

1.) 11=a|0-b|-1 ==> ab=12 ===> a=12/b
2. ) -1=a|6-b|