Answer:
x³y⁴
Explanation:
The Lowest Common Denominator of fractions is the Least Common Multiple of their denominators. That is, you want to find the LCM of ...
Find the highest power of each of the factors, and multiply those together.
The highest power of x is x³. The highest power of y is y⁴. So, the LCM of these expressions is ...
... x³y⁴
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Then the two fractions are ...
... 3y³/(x³y⁴) . . . and . . . 7x²/(x³y⁴)