How would you solve for x i cant remember right now 4x+6x=9x-10

Combine all of the x's on one side of the equation and then finish the problem!

So you are first going to want to combine the like terms (in this case, 4x + 6x = 10x) so that the equation is 10x = 9x-10. Next, subtract 9x from both sides. 
10x = 9x - 10
-9x    -9x 

 x    =   -10

Sometimes there are more steps, but in general, as long as you do the addition and subtraction before any multiplication, division, or exponential work, you will not have many problems.

  x =

Explanation:

Let's start the exercise with the definition of a system formed by the projectile and the block, in this case the forces during the collision are internal and the moment is conserved,

initial instant. Just before the crash

         p₀ = m v + 4m 0

final instant. Right after the crash, before the block began to move

        = (m + 4m) v_{f}

how the moment is preserved

        p₀ = p_{f}

        m v = 5m v_{f}

       v_{f} = v/5

knowing the speed of the system (projectile + block) we can use the relationship between work and energy

       W = ΔK

starting point. Just when the projectile + block system starts to move

       Em₀ = K = ½ m v_{f}²

final point. When the system is stopped

       Em_{f} = 0

The work of the friction force is

       W = - fr x

the negative sign is because the friction force opposes the motion, let's use Newton's second law to find the friction force

Y Axis  

      N- W = 0

      N = W = mg

The expression for the friction force is

      fr = μ N

     

substituting

     fr = μ mg

      W = - μ mg x

using the energy duty ratio

      - μ mg x = 0 - ½ m

        x =  

we substitute speed

       x =