Answer:
3(n +5)
Explanation:
You want the math expression that means "three times the sum of a number and five."
Sum
A sum is represented using a plus sign. "A number" is represented using a variable. "x" is a variable commonly used for an unknown value. "n" can also be used to represent "a number."
The sum of a number and 5 will be ...
n + 5
Times
We want an expression that is 3 times that sum, so we multiply it by 3:
3(n +5) . . . . . . 3 times the sum of a number and 5
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Additional comment
Note that the expression above is not the same as 3n+5, which would represent "the sum of 3 times a number and 5".