Translate: half a number decreased by 12

Which equation can be used to measure the density of water in a spherical water tank? let w represent the number of water particles within the region.

Astandard deck of cards contains 52 cards. one card is selected from the deck. (a) compute the probability of randomly selecting a diamond or heart. (type an integer or a decimal rounded to three decimal places as needed.) (b) compute the probability of randomly selecting a diamond or heart or club. (type an integer or a decimal rounded to three decimal places as needed.) (c) compute the probability of randomly selecting queen or club. (type an integer or a decimal rounded to three decimal places as needed.)

Idk math. i need to fill in the missing numbers . due tommorow !