Let's go through the words like this:
seven more than the product of three and some number.
Underline "some number":
seven more than the product of three and some number.
Replace "some number" by "x":
seven more than the product of three and x.
Underline "the product of three and x.
seven more than the product of three and x.
Replace "the product of three and x" by "3x":
seven more than 3x.
Now comes the hard part.
Ask yourself this question: How do you make something seven more?
The answer is: You write it down and then you put "+7" after it.
So you write down 3x and then you put "+7" after it.
Answer:
3x+7
Edwin