How can I rewrite the equation a - b = d using addition?

When you turn on a battery-operated device, an electrical circuit is

This is for my 8th grade science class, i really don’t understand. can someone me? , lol.

Two steel balls, each of mass m, are welded to a light rod of length l and negligible mass and are initially at rest on a smooth horizontal surface. a horizontal force of magnitude f is suddenly applied to the rod as shown. determine (a) the instantaneous acceleration a of the mass center g and (b) the corresponding rate at which the angular velocity of the assembly about g is changing with time.