So X is a variable meaning its a letter that represents a number. When there are a number and a variable (or a letter) like this 2x or 9y it means you are going to multiply the number by the variable. In this case it is 7 times x is equal to 21 so all we have to do is find what times 7 is equal to 21 and that number is 3. So if 7*x=21 is 7*3=21 then x=3. If you have any questions ill be more than open to answering them, hopefully this helped. Have a good day/night.
7x means 7 times a “mystery number” = 21 We can ask, “7 times what equals 21?”
The math family of equations here is 3 x 7 = 21 7 x 3 = 21 21 / 7 = 3 21 / 3 = 7
So to solve for x, or find out mystery number, we have 7x = 21 Whatever we do to one side of the equation, we have to do to the other side to keep it equal. Here, we’ll divide both sides by 7, so that on the left side, x is by itself. Then we have x = 21/7 which is x = 3
