For the graph y find both x-intercepts by solving the equation 3x^2 - 24x + 45 =0
3x^2 - 24x + 45 =0
first divide by 3 to simply
x^2 - 8x + 15 = 0
(x-3)(x-5) = 0
x = 3 or x = 5
check:
http://www.wolframalpha.com/input/?i=plot+y+%3D+3x%5E2+-+24x+%2B+45