Question

Segment AB = 4x - 10

Answer 1

To get to that AC = 68 you have to add AB and BC.
4x-10+12x+6=68 
Add your 4x and 12x together. 
Add -10 and 6 together. 
Your equation now is.
16x - 4 =68 
Add 4 to 68 
16x = 72
x = 4.5
Plug x into segment BC
12(4.5)+6
BC=60 <span />

Answer 2

(4x - 10) + (12x + 6) = 68
16x - 4 = 68
16 x = 72
x = 4.5

So, 12 (4.5) + 6 = 60