Since all three sides have the ( symbol it means that all the angles in the triangle are the same. In a triangle with all the angles congruent the side lengths are also congruent.
As such you can make an equation where one side length equals the other.
10x+3=3x+24
10x-3x=24-3
7x=21
x=3
then just substitute 3 for x
3(3)+24=KL
9+24=KL
33=KL
Also it took me forever to understand this concept, trust me it can easily get confusing. I hope this helps!
All three angles are marked in a way to indicate that they are equal. That means the side opposite them are also equal to another side of the same triangle.
