The answer would be a. 288. hope that helped
Given that ∠B ≅ ∠C.
to prove that the sides AB = AC
This can be done by the method of contradiction.
If possible let AB
=AC
Then either AB>AC or AB<AC
Case i: If AB>AC, then by triangle axiom, Angle C > angle B.
But since angle C = angle B, we get AB cannot be greater than AC
Case ii: If AB<AC, then by triangle axiom, Angle C < angle B.
But since angle C = angle B, we get AB cannot be less than AC
Conclusion:
Since AB cannot be greater than AC nor less than AC, we have only one possibility. that is AB =AC
Hence if angle B = angle C it follows that
AB = AC, and AB ≅ AC.
Answer: 
<u>Step-by-step explanation:</u>

NOTE: The sign between 4x and 7 is missing in the question you posted. I assumed it was 4x + 7 in order to solve the equation.
If she is making 6 costumes that need 3 7/9 yards each, the equation would be 6 x 3 7/9.
The answer to that equation would be 22 2/3.
How to get the answer:
3 x 6 = 18
7 x 6 = 42 (the seven is from the 7/9)
42/9 = 4 2/3
then add the eight teen and the 4 2/3 and you get 22 2/3.
65.52 will be the answer
Work: (10.4 * 12.6) ÷ 2