Final answer:
To evaluate the expression 21x where x = 4/7, multiply 21 by 4 to get 84 and then divide by 7 to obtain 12 as the simplest form of the answer.
Step-by-step explanation:
To evaluate the expression 21x for x = 4/7, you simply need to substitute the value of x into the expression. Here's how you do it step by step:
Write down the expression with the value to be substituted: 21 * (4/7).
Multiply 21 by 4 to get 84.
Divide 84 by 7 to get 12.
Therefore, the expression 21x evaluated at x = 4/7 is 12.
This is the answer in its simplest form.