Just in case a picture helps...

... where

... is the chain rule. Straight continuous lines differentiate downwards (integrate up) with respect to x, and the straight dashed line similarly but with respect to the dashed balloon expression (which is the inner function of the composite, which needs the chain rule).

This is called implicit differentiation, because you use the chain rule to differentiate y with respect to x. Solve the bottom row for y' i.e. dy/dx, and then plug in 4 for x and whatever values you are able to determine for y when x is 4, to get the two values of dy/dx at those points. That's the slopes of the tangents at those points, so multiply them by (what number?) to get the slopes perpendicular to those. Then you at least have the slopes of the normals. Then you can review the situation and see if you have the information to deduce the equations of these lines.

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