The arcs in the corners of the triangle mean that all 3 angles are the same.
Because the 3 angles are all the same this means that all 3 sides are also the same.
To solve for X, we can set 2 of the equations to equal each other and solve for x:
6x-3 = 3x +6
Add 3 to each side:
6x = 3x +9
Subtract 3x from each side:
3x = 9
Divide both sides by 3:
x = 9/3
X = 3
And if you replace x with 3 in each of the equations, they all equal 15.
