Find if f(x)= 2x^2 - 5x

When i add money am i supposed to make it like this 7+12 or 7.00+12.00 because i got 19 dollars for my answer

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?

Ineed with number 6 , explain how to get 1978