Answer:
The question is asking for you to type the formulas into the adjacent boxes. It wants you to be familiar with correctly typing formulas and using the underscore to type subscripts (the numbers that are smaller and are positioned lower than the letters). So, type out the formulas given into the boxes.
Na₂CO₃ would be typed as Na_2CO_3
Al₂(SO₄)₃ would be typed as Al_2(SO_4)_3