You know that BC is congruent to x so you need to solve for x using the ratio:

So then we need to find BC.
We know:


Therefore BC =8
Then:

Answer:
A, If you still need help
1.
(100 + d^2)(d + 10)(d - 10)
Use the rule of splitting perfect squares to get the factors.
2.
x^4y^8z^2(x^2z^6 - y)
The first term is the greatest common factor.