To find the max/ min of a function use the formula x = - b/2a
in the function x^2 - 6x +3, a would be the number in front of the x^2, since there is no number, a = 1. b is the number in front of x , which is -6, so b = -6
Now you have x = -(-6) /2(1) = 6/2 = 3
Now you have a value for x, replace it in the formula and solve:
3^2 - 6(3) + 3 = 9 -18 +3 = -6
The minimum is -6
The max of the graph is the highest point which is 12
The difference is 12 - -6 = 12 +6 = 18
The answer is 18