Question

f(x)=7x-4

a) f(0)

b) f(-3)

c) f(b)

d) f(x-1)

Answer 1

a)
for f(0), substitute x=0 in the expression f(x) = 7x-4 to get
f(0) = 7*(0) -4 =-4

and you can calculate similarly for the other questions.

Answer 2

what will i do for f(b) in problem c

Answer 3

As in (a), replace by what is in parentheses:
f(<b>x</b>) = 7*(<b>x</b>) -4
f(<b>b</b>) = 7*(<b>b</b>) -4

Do the same for (d), post to check your answer if you wish.

Answer 4

is it just any number i am asking

Answer 5

I am not too sure what exactly your question is.

But you can do the same for any number or expression. b is a variable the value of which is yet unknown, so you leave it at that.
For example, if f(x)=x²+4x+3, then
f(x+2)=(x+2)²+4(x+2)+3
=x²+8x+15