Question

Solve ƒ(x) = 2x – 11, what is the value of ƒ(6)

Answer 1

This shows a function of variable x
f(6) just means replace all x's in the function with 6's
so
f(x)=2x-11
becomes
f(6)=2(6)-11 . (notice 2x became 2(6) as it is multiplication)
= 12-11
=1

Hopefully this was clear for you, good luck