For this, think of the acronyms HIO and VOS
H, horozontal (movement)
I, inside (parenthesis)
O, opposite (sign)
and
V, verticle (movement)
O, outside (parenthesis)
S, same (sign)
To solve
f(x) is Y
f(x)= f(x) A vertivle translation 3 units up use VOS
f(x)=f(x+3)
f(x+3) A reflection across the y-axis, use HIO
f(x)=f(-x+3)
The final function is fx=f(-x+3)
if you need any extra help, i'd be glad to explain in the comments section