Answer: x^3y^4 is the lowest common denominator.
Step-by-step explanation: To get both expressions to have a common denominator, multiply both of them to get them equal. For the first expression, multiply the numerator and denominator by y^3: 3y^3/x^3y^4
The second expression should be multiplied by the numerator and denominator by x^2: 7x^2/x^3y^4
(Add exponents when multiplying them) Now both expressions have common denominators.