Hello there. To solve this question, we'll need to remember some properties about triangles.
First, the area of a right triangle as in the following drawing:
Can be calculated by the formula:
[tex]A=\frac{a\cdot b}{2}[/tex]If the area of the enclosed triangular region is greater than or equal to 60, we have the following inequality;
[tex]A\ge60[/tex]Now, using the lengths of the sides of the triangle, we'll have:
[tex]A=\frac{c\cdot12}{2}=6c[/tex]Therefore
[tex]6c\ge60[/tex]Divide both sides of the inequality by a factor of 6
[tex]c\ge10[/tex]The least possible value of c is 10 ft.