The solution for each equation is as follows:

1) Combining like terms in the equation X+3x=20:

X + 3x = 20

4x = 20

Divide by 4 on both sides:

x = 5

2) Solving the equation x+(x-20)+3x=180:

x + (x-20) + 3x = 180

5x - 20 = 180

Add 20 to both sides:

5x = 200

Divide by 5 on both sides:

x = 40

3) Simplifying the equation 3(x+20)-4x=10:

3(x+20) - 4x = 10

3x + 60 - 4x = 10

Combine like terms:

-x + 60 = 10

Subtract 60 from both sides:

-x = -50

Multiply by -1 on both sides:

x = 50

Therefore, the solutions for the given equations are x = 5, x = 40, and x = 50.