We can use the formula for the area of a triangle to solve for these dimensions.
The formula for the area of a triangle is [tex]A=\frac{1}2bh[/tex].
We know that the area of the triangle is 50, so here's our new equation: [tex]50=\frac{1}2bh[/tex]
How can we solve for [tex]b[/tex] and [tex]h[/tex]?
Well, we know how to solve equations with one variable.
And since the height is four times the base, we can replace [tex]h[/tex] with [tex]4b[/tex] and solve for b!
[tex]50=\frac{1}2b(4b)\\\\50=\frac{1}2(4b^2)\\\\ 50=2b^2 \\\\ 25=b^2 \\\\ \boxed{b=5\ ft}[/tex]
And of course, since the height is four times that, [tex]\boxed{h=20\ ft}[/tex]