Answer:
B
Explanation:
a-17=-15
so the whole point of solving problems like this is to get the variable on one side (a in this case) and the constants on the other side (-17 and -15 in this case).
so to get rid of the 17 because its negative you have to add 17 or do the inverse sign but whatever you do to on side you have to do to the other side so you add 17 to both side
-17+17 they cancel out
-15+17=2
so now we get that a=2
your answer would be B
hope this helps :D