Hey there Duolingocom4! :)
To solve this, you need to first input the value given for the variables:
[tex]mx-y [/tex]
is
[tex]1*5-2 [/tex]
Follow BEDMAS to simplify the expression.
[tex]5-2 [/tex]
[tex]=3[/tex]
The answer would be 3.
Hope this helps.
-Benjamin