Answer
$f(t)=(t+1)\sin (3t)$
Work Step by Step
We are given that $x=t-1$
Re-write as: $t=x+1$
When $a$ has a positive value then , shift the function to the right for $a$ units and when $a$ has a negative value then , shift the function to the left for $a$ units
Now, $f(t-1) =(t) \sin [3(t-1)] $ and $f(x)=(x+1)\sin (3x)$
So, we have the independent variable $t$ is: $f(t)=(t+1)\sin (3t)$
