"The sum of" means two or more numbers added together.
A number in this case can be represented by the letter 'n' as we don't know the value of the number.
Therefore, the sum of a number and six would be n + 6
Seven times the number would be 7n.
Hence, if they are equal to each other, in equation form it would be:
n + 6 = 7n
If you wanted to go a step further and work out what the number was, you could rearrange the equation:
n + 6 = 7n
6 = 7n - n
6 = 6n
1 = n
The number is 1.