Harry and ron set up this experiment with a glider, whose mass they have measured to be 565 g, and seven washers hanging from the string. if each washer has a mass of 12 g, what is the acceleration of the system, in m/s2

Let's call  the mass of the glider and  the total mass of the seven washers hanging from the string. 
The net force on the system is given by the weight of the hanging washers:

For Newton's second law, this net force is equal to the product between the total mass of the system (which is ) and the acceleration a:

So, if we equalize the two equations, we get

and from this we can find the acceleration:

Your answer is 1.5 hope i