Something something vague magic

Simplify a7/a4 a) 1/a3 b)-a/a2 c)a4/a3 d)a3

Yoku is putting on sunscreen. he uses 2\text{ ml}2 ml to cover 50\text{ cm}^250 cm 2 of his skin. he wants to know how many milliliters of sunscreen (c)(c) he needs to cover 325\text{ cm}^2325 cm 2 of his skin. how many milliliters of sunscreen does yoku need to cover 325 \text{ cm}^2325 cm 2 of his skin?

If you have the following equation, 2/3x+5/6-x=2-3/4x what would you multiply each term by to get rid of all the fractions