Beginning to sound very much like home/course-work ...
Look at the man pages for the commands you are being told to use:
For the ls command you will see that you will need the -l (long) option to provide file size information.
For the wc command you will see that you'll need the -c (character) option to have it could characters in the specified file name.
The question does not say how you are supposed to use the echo command to report on the file size comparisons, nor if you are to do this in a script or wholly from the command line. On that basis, and due to the fact that I don't have immediate access to a *nix system and this would all be from memory, I'll just suggest a method you can use.
Assign the results of the commands to a pair of variables, compare those variables and if they do not hold the same number, do the needed echo command. There are, of course, caveats - the ls -l command does not produce JUST the file size information - that appears as 'field' 5 (I think), so you'd need a way to just obtain that bit (hint: man awk, or man cut). Likewise, the wc command is likely not to just produce the number you are after. Try it by hand, see what it does and work out a way of getting just the data you need.
To assign the number to a variable, you'd have something like:
ls_filesize=$(ls -l myfilename | cut -f5)
You'd do something similar for the wc command, then to test to see if they are the same you'd have something like:
if [ $ls_filesize -ne wc_charcount ]
echo Commands produce different sizes