△ABC and △DEF are similar triangles. Triangle A B C has side lengths A B equals 12, B C not given, and C A equals x plus 7. Triangle D E F has side lengths D E equals x minus 4, E F equals x, and F D equals 5. Find BC. Hint: Solve for x first. There is another step after solving for x.

The answer of the above is

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First step is to get rid of the square root. remember that a square root is the same as raising to the (1/2) power. see below: multiply exponents per exponent rules to get: remember you subtract exponents from the denominator and add exponents in the numerator so: simplify further: so a is the correct choice. if you don't understand this google exponent rules and it will you understand. look at the image results.