2x - 3y = 3.....multiply by 4
5x - 4y = 4....multiply by -3
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8x - 12y = 12 (result of multiplying by 4)
-15x + 12y = -12 (result of multiplying by -3)
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- 7x = 0
x = 0 <===
2.16
Two negatives multiplied together make a positive, so it’s simply .9 x 2.4 which is 2.16

the equation is a quadratic one, and it has a positive coefficient on the leading term, meaning, is opening upwards, so it has a "burrow" for the vertex.
the minimum or lowest point for a quadratic opening upwards is, well, the vertex point :), the "x" value is the year, the "y" or f(x) value is the population, we're asked for the year, or the x-coordinate of the vertex
well
-4 because it is the lowest number you see and -4 is the value..?
2²-6x-56
this is unfactorable because there is no x on where the number is squared or the -56