1) 19.5 - 0.3x = 15.9

Subtract 19.5 from both sides:

-0.3x = -3.6

Divide by -0.3:

x = 12

2) (7 - 0.2x) * 1.4 = 7.56

Divide by 1.4:

7 - 0.2x = 5.4

Subtract 7 from both sides:

-0.2x = -1.6

Divide by -0.2:

x = 8

3) (6.1x - 13.2) ÷ 1.7 = 3

Multiply by 1.7:

6.1x - 13.2 = 3 * 1.7

6.1x - 13.2 = 5.1

Add 13.2 to both sides:

6.1x = 18.3

Divide by 6.1:

x = 3