SAT Question 9fc31513: Linear Equations In One Variable answer and explanation with Desmos solution

Choice C is correct. It's given that the perimeter of an isosceles triangle is $36$ feet and that each of the two congruent sides has a length of $10$ feet. The perimeter of a triangle is the sum of the lengths of its three sides. The equation $10+10+x=36$ can be used to represent this situation, where $x$ is the length, in feet, of the third side. Combining like terms on the left-hand side of this equation yields $20+x=36$. Subtracting $20$ from each side of this equation yields $x=16$. Therefore, the length, in feet, of the third side is $16$.