Three blocks are in contact and sitting on frictionless table. The first blog has a mass m1=1.2 KG, the second block has mass m2= 2.5 KG, and the third luck has mass m3 = 3.1 KG. An external force is applied causing three blocks to move together with the constant uniform acceleration od 1.9 m/s^2. What is the magnitude of the force exerted by the third block on the second block?