I have two main program called walk.cpp and useWalker.cpp which use the class I implemented. I have the class file Walker.h and Walker.cpp, and I am required to make a Makefile which contains the target walk, the target useWalker and a target all.
This is how my Makefile look like:

```
all:
    walk useWalker

//comment:sorry to delete the rest parts because it is a homework problem and I do not want my solution to be public. I will only keep the mistaken part.

```

And when I try to enter the command "make", there is an error message:
walk useWalker
make: walk: Command not found
Makefile:2: recipe for target 'all' failed
make: \*\*\* [all] Error 127

I don't know what mistake I made in my code to generate this error message and how to fix it??