To solve for x and y in the given equations, we need to isolate the variables.

1) 1/3x = 12
To solve for x, we need to multiply both sides by 3 to get rid of the fraction.
x = 12 * 3
x = 36

2) 2/3y = 9
To solve for y, we need to multiply both sides by 3/2 to get rid of the fraction.
y = 9 * (3/2)
y = 13.5

3) -4x = 1/7
To solve for x, we need to divide both sides by -4.
x = (1/7) / (-4)
x = -1/28