the goal seek will keep changing 1 cell until the value in the other cell is or is as close to the target as possible. But there has to be a formula in the target cell so that as excel changes the value in the other cell the target cell value will change. If there is no formula (that must somehow be dependent on the other cell) then it doesn't matter what excel changes the other cell to, it can't solve the problem. So in that image K13 needs some formula that changes based on the value put into K7.
