Can anybody help me with strategies in proofs?(Geometry)

Question

anonymous · Answer

heres one promblem, 
-8v + 6v – 8 = -8v + 8v + 8 you have to find the justification

parthkohli · Answer

What's $v$ here?

anonymous · Answer

what do you mean?

parthkohli · Answer

What do we have to do in this problem?

anonymous · Answer

your choosing if its Additive Inverse or Substitution Property or Given etc. Are you familiar with this?

anonymous · Answer

3 + 7a = -9

3 + 7a = -9	Given.
-3 + 3 + 7a = -3 + -9	Addition Property of Equality
0 + 7a = -12	Substitution Property of Equality
7a = -12	Additive Identity
7 over 7 times a equals negative 12 over 7	Division Property of Equality
1 a equals negative 12 over 7	Substitution Property of Equality
a equals negative 12 over 7	Multiplicative Identity 
these are some examples they gave me, but i dont understand.