Static electricity: charge, Coulomb's law and electric fields

Use this for “What is the electric field 0.30 m from a +2 μC charge, and the force on a 1 μC test charge there?”

Use this for “A +4 μC and a −2 μC charge are 0.5 m apart. What is the electric field 0.2 m from the +4 μC charge?”

Use this for “Two plates 3 mm apart have 12 V across them. What is the field between them, and the force on an electron there?”

Use this for “A charged rod is held near a metal can without touching it, and the can rolls toward it. Why?”