Question

I need the answer and the work! you have to find n.

Answer 1

Tell you what I'll do:  I'll show you the work, for two of them.
Then, knowing how to do it, you'll find the answers.
Deal ?

#1). n + (-13) = -12

Remove the parentheses
on the left side:                     n - 13 = -12

Add  13  to each side:           n        =    1

================================

#3).                        -15 + n  =  3

Add  15  to each side:     n  =  18


OK.  Look those over, understand how they're done, then TAKE IT !