I put this into good old Desmos since I couldn't figure it out by hand. So here is what I got.
Y= -5.3x + c
-7.1= -5.3(-2.4) + c
C= -12.72-7.1 = −19.82
Y= —5.3x-19.82
Using the distance formula:
AB^2 = (-2-6)^2 = (2-2)^2
= 64
AB = 8 units
BC^2 = (6-0)^2 + (2-8)^2
= 36 + 36
= 72
BC = 6 root 2
AC^2 = (-2-0)^2 + (2-8)^2
= 4 + 36
= 40
AC = 2 root 10
Perimeter = 8 + 6 root 2 + 2 root 10
= 2 (4 + 3 root 2 + root 10) units
Six million, seven hundred and thirty five thousand, eight hundred and thirty four
hope this helps :)