Your questions are rational expressions.
Essentially, you are adding/subtracting fractions with unknown values (i.e. the variable x).
If you want to add/subtract these, you need a common denominator. Just like you find a CD in 1/2 + 1/3, you have to find a CD between x^2 + x and x (question 20).
Rearranging gives us x(x + 1) and x. Now to find a common denominator, we multiply both the denominator by (x + 1), so now our denominators are both x(x+1) (common). Except that if we multiply on the denominator, we must also multiply on the numerator.
After doing these steps, you can finally add the numerator. Same concept with subtraction.
I hope this helps!