Answer: D. 21t²y
Explanation:
Step 1: Distribute the numbers and variables inside the parentheses:
(7ty)(3t) = 7ty * 3t
Step 2: Multiply the coefficients (numbers) together:
7 * 3 = 21
Step 3: Multiply the variables with the same base (t) together by adding their exponents:
ty * t = t^(1+1) = t^2
So, the simplified expression is:
21t²y
Therefore, the correct answer is:
D. 21t²y