Evaluate this function when f (x) x=3

f (x) = 4x+6

the answer is 10 but I don't know how it got this.

Evaluate this function when f (x) x=3

f (x) = 4x+6

Important! The "x" is just a place-holder! And "f" is just a name.

Just replace the variable "x" with "3":

FOR x = 3

f (3) = 4*3+6

f (3) = 12+6

f (3) = 18

The answer is 18 NOT 10 (as you said).