Question

Trying to write an equation for line on graph without any numbers given to plug into for slope

Answer 1

In that situation, you use the information you DO have.  It's not always
enough to do the job.  But often it is, and in that case, you use what you
do have to answer the question or solve the problem.

Sadly, I can't be any more specific than that.  You haven't told us what
information you do have ... only what information you don't have.