We are asked to formulate an algebraic expression for the statement "The sum of 5 and three times a number is 23", first a "sum" is mentioned and it says that the result is 23, let's say that we are adding two numbers a and b and we get 23, like this:
a + b = 23
From the statement we know that one of the numbers that is being added is 5, then by using 5 instead of a, we get:
5 + b = 23
And we are told that the other number that is being added is being multipliend by 3, by replacing 3x (three times a number "x") for b we get:
5 + 3x = 23
Then, the answer is 5 + 3x = 23