To solve the first equation, 3y - 4 = 3y/7:

Subtract 3y from both sides to isolate the variable y:
3y - 3y - 4 = 3y/7 - 3y
-4 = -4y/7

Multiply both sides by -7 to get rid of the fraction:
-4 * -7 = -4y
28 = 4y

Divide by 4 to solve for y:
y = 28/4
y = 7

Therefore, the solution for the first equation is y = 7.

To solve the second equation, b/5 - 2b = -4:

Multiply all terms by 5 to get rid of the fraction:
5 (b/5) - 5 2b = 5 * -4
b - 10b = -20

Combine like terms:
-9b = -20

Divide by -9 to solve for b:
b = -20/-9
b ≈ 2.22

Therefore, the solution for the second equation is b ≈ 2.22.