The standard deviation of 36,18,12,10 and 9 is 10

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
18 divided by 60 = 0.3
0.3 x 100 = 30
18 is 30% of 60
Every angle of a square equals 90 degrees.
2x - 4 = 90 3y + 6 = 90
2x = 90 + 4 3y = 90 - 6
2x = 94 3y = 84
x = 94/2 y = 84/3
x = 47 y = 28
so x = 47 and y = 28