the minus sign outside of the parentheses can actually be represented with -1 instead.
this means that you must distribute (multiply) -1 by the numbers inside of the parentheses.
keep in mind that when you multiply the -1 by the 2nd number inside, and the operation is subtract, instead of 17b, it would be -17b.
-1 • 18a = -18a
-1 • -17b = -17b
the final answer would be -18a + 17b :)
