Answer:
f(5) = 10, but I didn't need to do synthetic division to get there. So I may misunderstand the problem.
Explanation:
f(x) = 3x^2 - 9x - 20
f(5) = 3 (5)^2 - 9*5 - 20
f(5) = 75 - 45 - 20
f(5) = 10
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