There can only be two definite x-intercepts, so your goal it to find 2 numbers of x that, when plugged into the equation, give you the answer of 0. 1 is the first x-intercept(4-24+20 equals 0). The second one is 5 (100-120+20 equals 0). So the average is 3, so the axis of symmetry is 3 since 5+1=6, and 6/2=3
Honestly, there is an easier way to find the axis of symmetry. the equation would be -b/2a, where as b is the coefficient in the second part of the equation, while a is the first coefficient in the equation. -(-24) is 24, and 4*2=8, so 24/8=3
I hope I actually answered this the way you wanted. You asked for an equation, but I just answered the axis of symmetry with very simple equation initially and another equation
You have -4,-3,-2, that is a 3 out of a total of 21 points or numbers on the number line. 3/21 is reduces to 1/7.
3 goes into 21 , 7 times. That is why it reduces to 1/7.