{
  "problem": "Solve for $x$ and $y$ using substitution. ${3x-y = -9}$ ${y = -5x-7}$",
  "hints": [
    "Since",
    "$y$",
    "has already been solved for, substitute",
    "$-5x-7$",
    "for",
    "$y$",
    "in the first equation.",
    "${3x - }{(-5x-7)}{= -9}$",
    "Simplify and solve for",
    "$x$",
    "$3x+5x + 7 = -9$",
    "$8x+7 = -9$",
    "$8x+7{-7} = -9{-7}$",
    "$8x = -16$",
    "$\\dfrac{8x}{{8}} = \\dfrac{-16}{{8}}$",
    "${x = -2}$",
    "Now that you know",
    "${x = -2}$",
    ", plug it back into",
    "$\\thinspace {y = -5x-7}\\thinspace$",
    "to find",
    "$y$",
    "${y = -5}{(-2)}{ - 7}$",
    "$y = 10 - 7$",
    "$y = 3$",
    "You can also plug ${x = -2}$ into $\\thinspace {3x-y = -9}\\thinspace$ and get the same answer for $y$ : ${3}{(-2)}{ - y = -9}$ ${y = 3}$"
  ]
}
{'source': 'AMPS', 'file': 'amps/khan/508/1608016202.json'}