The entry "-7/8m=1/4" can be interpreted in a variety of ways... such as "(-7/8)m=1/4" or "-7/(8m)=1/4", etc. 

I believe the difficulty you have encountered is how to enter the 'm' outside of the fraction, so use either the "right arrow key" or use a click from the mouse to move the cursor outside the fraction. 

I would also recommend that a solution begins with 'a few steps' (see the 'Options' tab) and then request for additional steps as the extra information is helpful.