Its an absurd decimal, which I'm pretty sure you don't want but will give to you anyway. Its roughly 0.02631578947...
What I’m support to fine it in the graph or find the slop, solve for x or y???? Put the whole question so I can help you
5a - 4a = -9 - 8a
a = -9 - 8a
9a = -9
a = -1
36.8%. divide 28.52 by 77.5 then multiply by 100