x = 9
Step-by-step explanation:
The angles in red are equivalent and the triangle is isosceles.
This means the sides with lengths 12 and x + 3 are equivalent.
x + 3 = 12
x + 3 - 3 = 12 - 3
:)
9
because isocelese triangle have 2 congruent and sence 9+3 =12 then the answer is 9
hope this helped:)