If the force is f=-30 units and the acceleration is a=6 units, find the mass, m

According to Newton's law:

Force = mass * acceleration

The force is given as - 30 units (the negative sign only indicates the direction)

The acceleration is given as 6 units

Substitute is the above equation to get the mass as follows:

30 = 6*mass

mass = 30/6 = 5 units