Cheryl writes 7 fewer posts than Kevin on a social media site. Answer the questions to write an algebraic expression. Then evaluate the expression for the given value, 1. Choose a variable to represent the number of posts Kevin writes. Explain why you chose this variable. 2. Which operation ( addition, subtraction, multiplication, or division ) applies to this situation? Justify your choice. 3. Use your variable and the operation you identified to write an expression for the number of post Cheryl wrote. 4. If Kevin wrote 21 post, how many did Cheryl write.​