To solve the equations:

1) X - 1/2 = 3/4x

First, get rid of the fractions by multiplying everything by 4 to get:
4x - 2 = 3x

Subtract 3x from both sides:
x = -2

2) 1 4/5y = y + 4

First, convert 1 4/5 to an improper fraction:
1 4/5 = 9/5

Now, substitute back into the equation:
9/5y = y + 4

Get rid of the fractions by multiplying everything by 5 to get:
9y = 5y + 20

Subtract 5y from both sides:
4y = 20

Divide by 4:
y = 5

3) 3/4y - 2/3 = 7/12y

First, get rid of the fractions by multiplying everything by 12 to get:
9y - 8 = 7y

Subtract 7y from both sides:
2y - 8 = 0

Add 8 to both sides:
2y = 8

Divide by 2:
y = 4

Therefore, the solutions are:
1) x = -2
2) y = 5
3) y = 4