In the equation y=3t^2 - 7x + 4

I got the x-intercept points as -8 and -8.33

But then got the turning point co-ordinates as 1.17, -0.08
using the x=-b/2a formula then substituting into the quadratic equation.

This doesn't seem like the correct answer, could someone please let me know what I have done wrong?

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Kind regards,
James