Answer:  

Explanation:
 Let be "x" the number mentioned in the exercise.
 "Seven times a number" indicates a multiplication. Then, this can be written in this form:
 

 And "Six time the number" is:
 

Finally, it is important to remember that the sum of two numbers is obtained by adding them. In this case the exercise says "The sum of seven times a number, and 3, is equal to six times the number", therefore, we can write the following expression:
 
