Find the equations of the straight lines a, b, c

See, pls, the suggested decision:
1) the lines seem to be parallel, a||b||c. Using this property,
2) two points are clear for line 'a': (0;0) and (6;1). Equation is  
3) for lines 'b' it is additional +4 points in vertical direction (upon line 'a'): 
4) line item 3 for line 'c' is additional (-4) points in vertical direction (below line 'a'):  

Absolute value graph shifted point 5 up