Final answer:
To simplify the expression, we can represent the number as 'x'. Adding 3 to 'x' gives us 'x + 3'. Multiplying it by 7 can be written as '7(x + 3)'.
Step-by-step explanation:
To simplify the expression 'If you think of a number, add 3 to it, and multiply it by 7' using algebraic expressions, we can represent the number as 'x'. Adding 3 to 'x' gives us 'x + 3'. Multiplying it by 7 can be written as '7(x + 3)'. Therefore, the correct algebraic expression is option A: 7(x + 3).