Question

need help. i think did something wrong.
i need to convert this to an equation.
"Each interior angle of a regular polygon is 90 less than 5 times the measure of each exterior angle. How many sides does the polygon have?"

so this is how i got it
5(360/x) - 9 = (x-2)180/x
5(360) - 9x = 180x - 360
1800 - 9x = 180x - 360
1800 + 360 = 180x + 9x
2160 = 189x
11.43 = x

i find it wrong cuz i need to find the number of sides. pls. i need to knw asap :(