Hello!
I think what they asking here is to simply solve the point-slope formula for x, so we have;
y-y1=m(x-x1)
(y-y1)/m=x-x1
((y-y1)/m)+x1= x
So now we have x in terms of m,x1,y,y1
Hope this helps you out. Any questions please feel free to ask. Thank you.