N.b., this is copied from an answer I wrote for someone else.Thinking about the graph of y, the rate of change is zero whenever there is an extremum.
First, differentiate y.
Next, find the zeros of y' by factoring.
Now, we substitute these x-values into the
original equation to find the coordinates.
Hopefully this makes sense!
Answer:
65
because 22 + 63 equals 85 and 20+65 equals 85 as well.
hope it helps :)