Need help will give thanks or brainliest

Answer:
6 cm
Step-by-step explanation:
Well let me explain... It's saying that side AB has a length of 6 cm and side BC has a length of 10 cm. So we can already start labeling the sides with their given length and actually solve for AC.
Well we don't really got much to say about AC but what we do know is that side AB and AC are equivalent. Why? Cause when there's always a triangle that has two equal sides but one side bigger, the triangle is a isosceles.
So we can say that side AB is (Δ) from the top of the triangle all the way to the left corner (6 cm). Then side BC will be from the left corner to the right corner (10 cm) and side AC will be from the top to the right corner (6 cm).