Step-by-step explanation:
It is an isosceles triangle , it has two equal angles both 55°.
All Isosceles triangles have two equal angles and two equal sides.
So in this case x +18 is equal to 3x, and to find x you will equal them to each other to create a linear equation and solve.
x + 18 = 3x
x - 3x = -18
-2x = -18
× = -18 / -2
× = 9 (ans)
Hope I was able to help. Good Luck :)))
