Simplify. your answer should contain only positive exponents

xy^2 * 2y^4 * 4yx^-1

how do do this? i forget.

Since the first few terms have only positive exponents, create a fraction by putting them over one. For the last term the x has a negative exponent so you should bring it to the denominator (the variable with the attached exponent only) and rewrite the negative exponent as positive so it becomes 4y/x^1. Then multiply the three together as you would multiply fractions.