A 25kg object moves from left to right at a speed of 30km/h. What net force is required to keep this object moving in a straight line at constant speed

Note that from Newton's law of motion:

the sum of the positive horizontal forces on an object equals the sum of the negative horizontal forces therefore, the net force on the object is zero.

Also, velocity is constant, acceleration is zero.

F = m * a

= 0 N