The correct answer is (C).
Getting to the Answer: To find the product of two terms, multiply each individual piece together. Thus, (2x4y)(3x5y8)=(2x3)(x4x x5)(y x y8). To multiply two exponents that have the same base, add the exponents. Since y=y1, the expression can be written as 6x4+5y1+8, which simplifies to 6xy9.
(A) Incorrect: this is the result of adding 2 + 3 instead of multiplying 2 x 3
(B) Incorrect: this treats y as y0
(C) Correct: this matches the correct calculation
(D) Incorrect: this multiplies the exponents of x and of y rather than adding them and adds 2 + 3 rather than multiplying them
(E) Incorrect: this multiplies the exponents of x and of y rather than adding them