How you start the equation is by plugging
3
into both of the
x
's in the problem to make it:
f
(
3
)
=
3
(
3
)
−
4
Next, you multiply the
3
(
3
)
to get
9
and subtract
4
. So in the end, you leave the
f
(
3
)
and
9
−
4 is
5
, so the
y
in the equation is
5
.
The answer would be written as
f
(
3
)
=
5
