Zinc sulfate vs zinc gluconate?

Can somebody please help me understand. Im trying to supplement Zinc, but im scared of overdosing (yes im ignorant to this whole thing) My Multivitamin has 20mg of zinc sulfate...and my zinc supplement has 50 mg of zinc gluconate. 1.What's the difference between the 2? 2. Can you mix those together safely? 3. How many MG of Zinc is in each (how much zinc would i consume if i took one of each) please help