is there any sign between 12 and -17 on the left side?
if no, then this is to be interpreted as a multiplication and is equal to -204.
so we have -204=-17+k
which means
-204+17=k
-187=k
so k is -187
if thre is a plus between the 12 and (-17) then k would be 12 (and both sides of the equation would be essentially the same, just inverted order)