What are your "decision variables" (the values for the "by changing" field)? I would guess it is the amount of each ingredient, but I don't want to assume too much. Also, what, exactly do you mean by "the ratio of jar to the rest is 0.25"? 0.25=jar/(foo+bar) or 0.25=jar/(foo+bar+jar) or something else.

You could add an additional "objective function" that computes the ratio of "jar" to "foo+bar" and then add a constraint for the cell that contains this secondary objective function =0.25 in Solver.

If your ratio is something like the equations I have above, I would probably take jar out of the list of decision variables and make it a straight up calculated value. jar=0.25*(foo+bar) for example. Then, as foo and bar are adjusted, the ratio of jar to foo+bar will be fixed by this formula.