+130081 Here's the key
Simplify both sides
If one side = the other side, we have infinite solutions
(Hint : look at the first one)
An equation can have infinite solutions if the variables go away and you are left with something like "5 = 5" or "7 = 7".
I believe that the first equation leaves you with -7 = -7 for any number "n". (This has infinite solutions)
The second equation leaves: -15 = 10. No value of "n" works for this. (This has no solutions)
The third equation leaves: -3 = 10. (This also has no solutions)
The last equation leaves you with n = 2. (This is only one solution.)
