y = 3 t^6 − 7 √t + 9/t

y'=

Just use the rule for taking the derivatve of a t^n, where a is a constant. The rule is:

d/dt(a*t^n) = a*n*t^(n-1)

Then add up the three terms.

The derivative of 9/t (which is 9*t^-1) is -9t^(-2)

You do the rest