The given phrase is,
" The product of 3 and the sum of 7 and s.​"
Here it is saying that the product of 3, so, 3 is being multiplued with a certain value.
This can be expressed as,

The product of 3 and the sum of 7 and s
The sum of 7 and s can be expressed as,

The product of 3 and the sum of 7 and s can be therefore, written as,

Thus, the answer is 3(7+s)