Question

let f(x) =4x^4-6 evaluate f(3)

Answer 1

Raise 3 to the fourth power (giving you 81), multiply the result by 4, and subtract 6 from the result.

Surely you can do that on your own.

Answer 2

you should be familiar with the terminology of this topic
if f(x) = 4x^4 - 6
f(3) = 4(3^4) - 6
= 4(81) - 6
= 324-6
= 318 , (simply replace the x with 3 in the expression)

BTW, why did you label this question under the topic of "trig" ???