19
If she has already watched 1.5 hours and she can only watch 5 hours per week, then we have the inequality:
1.5 + T ≤ 5
where T is is the number of hours she can watch more before reaching her limit

20
If he needs 100 points, already has 40 and earns 2 for every movie, we have the inequality:
40 + 2m ≥ 100
where m is the number of movies he needs to watch

21
We can have the equation:
x + 1 = x + 2 – 1
This would result to:
x + 1 = x + 1
which have the same terms on both sides.
Further, the equation would be:
0 = 0