Read and study Reiny's reply.
https://www.jiskha.com/display.cgi?id=1504542568
@Alex asked this question when I was on earlier: Let line l_1 be the graph of 5x + 8y = -9. Line l_2 is perpendicular to line l_1 and passes through the point (10,10). If line l_2 is the graph of the equation y=mx +b, then find m+b. I'm wondering like how everyone did it and is this pre-algebra, algebra 1, algebra 2, geometry, pre-calculus, or calculus. Thank you for answering!
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I think algebra 1 is points and slopes
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