I have such a question: - at what value of t does the local maxima of f(t) occur?

so, my attempts in the base of the part 1 of the FTC I have

, since the denominator would never be I evaluated the numerator

which gave me two critical points , and evaluating the f''(t) at those points gave me (-4) > 0 , and local maxima, but it actually is considered wrong in my homework,

what did I miss here?