Original equation was y = x², which in this form looks like
y = 1(x - 0)² + 0
If the shape of the graph didn't change, that means that a (the compressor/intensifier) stayed the same (a - value) meaning we can write the equation as..
y = (x-h)² + k
Remember, (h, k) is the vertex, which looking from your graph is at (4, 1)
just pick an even denominator and take half of that number for the numerator. This only works because the most basic form of 4/8 is 1/2. This method only works if your selected fraction is equivalent to 1/2.