a)

2x + x – 3 – 4x = 5x + 9

–x – 3 = 5x + 9

–x – 5x = 9 + 3

–6x = 12     / : (–6)  

x = –2

b)   

x + 2(x – 5) = 7 – (x – 1)

x + 2x – 10 = 7 – x + 1

3x – 10 = 8 – x

3x + x = 8 + 10

4x = 18     / : 4          

x = 4,5

c) 

2x + 7(2 – x) = 3(2 –