Question 406438
You know that combined, there are 33 items on two grocery lists. 
Let's have the first grocery list be "x" and the second grocery list be "x+7", as the equation states that the number of items differs by 7. 
Now you just have to add them together to find out how much one equals. 
(x)+(x+7)=33
Combine your like terms, the variable first(x). 
2x+7=33
Since your ultimate goal with an equation is to get the variable on one side or the other without any numbers before or around it, you'll want to get rid of the 7 next to the 2x by canceling it out with the number on the other side. Subtract both sides by 7. 
2x=26
Divide both sides by 2 to get the 2 away from the variable.
x=13
Now plug in your answer to both of your variable values. 
x=13
x+7=20
Check this by plugging it into your equation. 
(13)+(20)=33
33=33
Voila. 
Hope this helps!