Mathematical equations (level 1)

First of all, I would like to give to the people who are interested in mathematics some mathematical exercises about equations.

Level 1 (very simple equations):
Solve the following equations:
x + 5 = 20
x + 8 = 25
7 + x = 10
25 + x = 50

Challenge exercise 1:
Prove that the equations
x + 7 = 15 (1)
y + 12 = 20 (2)
have the same solutions.

Solve the following equations:
20 - x = 15
12 - x = 7
x - 5 = 20
x - 16 = 32

Challenge exercise 2:
Find which equation's solution is greater than:
20 + x = 13
y - 4 = 21
z + 5 = 19

Coming soon with more exercises!
Feel free to comment!