The answer is going to be: answer B.
Hope this helps =D
First, let x or any variable represent the number of paintings Kate initially has. After selling 12 of it, her paintings now becomes only x - 12. Then, she purchased 7 more making the number of her paintings become x - 12 + 7 = x - 5. This number tantamount to 21.
x - 5 = 21 ; x = 26
Thus, Kate initially had 26 paintings.
2x+4x-4=2+4x
2x+4x-4x=2+4
2x=6
x=3
25-x=15-3x-10
3x-x= 15-10-25
2x= -20
x= -10
4x=2x+2x+5x-5x
2x+2x+5x-5x-4x
0 . no solution