f(t) = sqrt(6)/t^4
f(t) = sqrt(6) *[t^(-4)]
f'(t) = sqrt(6)*[(-4)*t^(-5)]
f'(t) = -4*sqrt(6) *[t^(-5)]
f'(t) = -4sqrt(6) / t^5
That is it.
But more importantly, how do you get this answer?
The squareroot of 6 is a constant, so you can bring just multiply that constant to the answer at the end.
Now you have this:
From here, it's a simple power rule problem.