The sum of one and the product of 4 and a number x

1 + 4x

Step-by-step explanation:

Let's break this down.

"The sum of one" means that something is being added to the number one:

1 +

"and" whatever comes after the word 'and' will be added to the number one

"the product of 4 and a number x" this means that the number four and the variable x are being multiplied:

4x

Put it together:

1 + 4x

Therefore, the expression is 1 + 4x.