Assuming that we need to solve the equation 5x +3 = 4x for x we have:

5x +3 = 4x

5x - 4x = - 3

x = -3

Indeed, if we plug x = -3 in 5x + 3 = 4x we get equality:

5*(-3) + 3 = - 15 + 3 = -12 = 4*(-3)

The solution for x is -3.