don't report what you don't understand
the x value of the vertex of the parabola in form
y=ax^2+bx+c
is -b/2a
given
y=6x^2-72x+220
x value of vertex is -(-72)/(2*6)=72/12=6
xvalue is 6
sub that for x in the equation
y=6(6)^2-72(6)+220
y=216-432+220
y=4
(x,y)
vertex is (6,4)