I don't have a visual I can provide, but the ratio of the areas is the square of the ratio of the perimeters of a 2D figure.
Intuitively, you can imagine that the triangle is simply being "scaled up" by a factor of 7/3, so the base scales up to 7/3 its original length and the height becomes 7/3 its original height.
Therefore, the new ratio is the square of the ratio of the perimeters, which is 9:49.
