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The denominators of the two added terms can be written x(x-3). The x^2-6x term can be written x(x-6). Therefore
(x^2 + 11x)/(x^2 - 3x) + (x^2 - 6x)/(x^2 - 3x) = [x(x+11) + x(x-6)]/[(x(x-3)]
Cancel out the x terms and you get
(2x-5)/(x-3)