Yes you can and if you ask at the office they will tell you what number to catch. A taxi will cost 40,000 to 60,000d depending on which route the driver takes. About $2 - $3
Now about the Zoo. Please be prepared to be truly disturbed by the conditions the animals are caged in. It is far removed from the modern zoos in Australia.
The 5 yrs I have lived here I have still not visited the zoo. I did research first and decided I like animals too much to want to see them under distressing conditions. I have dropped off Aussie friends and when I went to collect them they said why don't I warn them? So now I do.
Warm regards and travel safe in Vietnam