Next time please indicate which problem you want to work on.
One example of an equation with variables present on both sides is
y-b = m(x-a). Given the slope of a line and one point (a,b) through which the line passes, you can come up with an equation of the line.
Or, given the numeric value of y-b and that of x-a, you could obtain the slope of the line thru the points (x,y) and (a,b).