Let's assume
that number as y
the product of 7 and a number means multiplication of 7 and y
so,
the product of 7 and a number=7y
the sum of 10 and the product of 7 and a number means addition of 10 and 7y
so, we get
the sum of 10 and the product of 7 and a number is 10+7y
so, option-C.........Answer