1st one The question is asking to states on how can graphing be applied to solving systems of non-linear equation. I would say that when you have non linear equation and plot them, you can obtains the points where those function intersect, so they are possible solution. Constraints could be use as guide line or model.
2ND one
When you look at a graph, you can only guess at an approximation to the solution. Unless the solutions points are nice neat numbers (and unless you happen to know this in advance), you can't get the solution from the picture
I hopes this helps!!!!!!!!!!!!
