Initial speed of the skateboard (u) = 0 m/s (Starts from rest)
Acceleration of the skateboard (a) = 2 m/s²
Time taken by the skateboard (t) = 2s
By using equation of motion, we get:

Final speed of the skateboard(v) = 4 m/s
Linear is correct credit to the person above
To start, you need to subtract 4x from both sides, that way, x is one one sid of the equation.