`a) x/3 = y/8 = `$\dfrac{x - y}{3 - 8}$` = 85/-5 = -17.`
`+) x/3 = -17 => x = -51.`
`+) y/8 = -17 => y = -136.`
`b) 4x = 10y => x/10 = y/4`
`=> `$\dfrac{2x}{20}$` = y/4 = `$\dfrac{2x + 4}{20 + 4}$` = -48/24 = -2.`
`+) `$\dfrac{2x}{20}$` = -2 => 2x = -20 => x = -10.`
`+) y/4 = -2 => y = -8.`
