To subtract vectors, you simply have to subtract correspondent coordinates.
So, if you have
[tex]u = \langle u_1,\ u_2,\ldots u_n\rangle ,\quad v = \langle v_1,\ v_2,\ldots v_n\rangle [/tex]
the subtraction is simply
[tex]u-v = \langle u_1-v_1,\ u_2-v_2,\ldots u_n-v_n\rangle [/tex]
So, in your case, we have
[tex]\langle-9,4\rangle-\langle 8,-5\rangle=\langle -9-8, 4+5\rangle=\langle -17,9\rangle[/tex]
